Cardiovascular question bank

B. Blockade of β2 receptors, removing cAMP-mediated relaxation of bronchial smooth muscle — β2 activation raises cAMP and activates PKA to relax bronchial smooth muscle. Non-selective propranolol blocks it, causing passive bronchoconstriction and interfering with exogenous bronchodilators such as albuterol; a rise in cAMP would relax the airway, not constrict it. Propranolol has no other autonomic activity (it does not stimulate α1 receptors), its membrane action appears only above β-blocking doses, and β1 receptors sit mainly in the heart — which is why β1-selective agents lower FEV1 less.

D. Activating a Gs-coupled receptor distinct from the β receptor, raising cAMP through adenylyl cyclase — This is β-blocker toxicity: bradycardia, hypotension and hypoglycemia, with seizures because lipophilic propranolol enters the brain. Glucagon is the antidote. It binds its own Gαs-coupled receptor, raising cAMP via adenylate cyclase and activating PKA independently of the β-adrenergic binding site. β-agonists must compete with the blocker, and overdose can resist adrenergic agents; raising cAMP by phosphodiesterase inhibition is how inamrinone and milrinone work; muscarinic blockade is atropine, which has already failed; and sodium-channel blockade (membrane-stabilizing activity) is a cause of QRS widening in overdose, not a treatment.

E. Several-fold higher metoprolol levels, with loss of β1 selectivity — Metoprolol is cleared mainly by hepatic CYP2D6. Poor metabolizers reach several-fold higher concentrations, which deepens β1 blockade (bradycardia) and erodes cardioselectivity (β2 blockade, wheeze). Its metabolites appear to have no β-blocking activity, less than 5% of an oral dose is excreted unchanged, it has no ISA, and the α-blocking R(+) enantiomer belongs to carvedilol. CPIC advises starting poor metabolizers at the lowest recommended dose with careful titration and closer monitoring for bradycardia, or choosing another β-blocker.

D. Pindolol — Pindolol is a non-selective β-blocker with intrinsic sympathomimetic activity. As a partial agonist acting directly at the receptor, it still blunts exercise and isoproterenol tachycardia but lowers resting heart rate and resting cardiac output less than drugs lacking ISA. Atenolol, metoprolol, nadolol and propranolol have no ISA. Acebutolol also has ISA, but milder: about 3 beats/min less resting slowing.

C. Hydrolyzed by esterases in red-cell cytosol — Esmolol is metabolized by hydrolysis of its ester linkage, chiefly by esterases in red-cell cytosol — not by plasma cholinesterase or red-cell membrane acetylcholinesterase. Its clearance exceeds cardiac output, so it does not depend on liver or kidney blood flow, and no special precautions are needed in hepatic impairment. The elimination half-life is about 9 minutes, with substantial recovery from blockade 10–20 minutes after the infusion stops.

E. Isoproterenol — Isoproterenol is a nonselective β agonist with very low α affinity. β1 raises heart rate and contractility, while β2 lowers peripheral resistance, so diastolic and usually mean pressure fall and systolic pressure may stay the same. Phenylephrine and norepinephrine raise resistance (with reflex slowing), vasopressin acts on V1 receptors, and midodrine is oral.

D. Phosphodiesterase 3 — Milrinone selectively inhibits the peak III (PDE3) cAMP phosphodiesterase in cardiac and vascular muscle. cAMP accumulates, increasing contractility in the heart and relaxing vascular muscle — an inotrope and vasodilator. It is not a β agonist and does not inhibit the Na⁺/K⁺-ATPase as digoxin does.

B. Baroreceptor-mediated increase in vagal activity — Phenylephrine is a pure α1 agonist. As mean arterial pressure rises, vagal activity increases and causes reflex bradycardia. It has no β-blocking action; the slowing is a reflex response to the rise in pressure.

C. Sleep with the head of the bed raised and take doses only in the upright daytime hours — Midodrine’s active metabolite, desglymidodrine, is an α1 agonist that raises supine as well as standing pressure (boxed warning). Supine hypertension is controlled by not lying fully flat (head of the bed elevated) and by dosing during the day — not after the evening meal or within about 4 hours of bedtime. The scalp tingling and goosebumps are pilomotor α1 effects.

A. V1 receptors coupled to Gq/11, phospholipase C and IP3, releasing intracellular calcium — Vasopressin constricts vessels through V1 receptors on vascular smooth muscle coupled to the Gq/11–phospholipase C–IP3 pathway, releasing intracellular calcium. Its V2 receptors (adenylyl cyclase) mediate antidiuresis instead. In vasodilatory shock it raises systemic resistance and pressure and reduces norepinephrine requirements.

B. Reduced degradation of bradykinin, increasing submucosal vascular permeability — ACE (kininase II) degrades bradykinin, so ACE inhibition lets bradykinin accumulate and raise submucosal vascular permeability. Bradykinin-mediated angioedema lacks urticaria and itching and often resists antihistamines, glucocorticoids and epinephrine — unlike histamine-mediated swelling. It can appear at any time (median onset 1–2 years) and is about 4 times as common in Black patients. Hereditary C1-inhibitor deficiency is a different, excess-production form of bradykinin angioedema; ACE inhibitors lower angiotensin II rather than raise it; and lisinopril inhibits ACE — AT1-receptor blockade is how ARBs work.

A. Loss of angiotensin II–mediated efferent arteriolar constriction that was maintaining GFR — In bilateral renal artery stenosis, filtration depends on angiotensin II constricting the efferent arteriole. ACE inhibition removes that tone, intraglomerular pressure falls, and GFR drops; a creatinine rise above 30% should prompt a search for bilateral stenosis or volume depletion. ACE inhibitors lower aldosterone and angiotensin II rather than raise them. Bradykinin dilates vessels rather than constricting them. Losing angiotensin II feedback raises plasma renin activity instead of suppressing renin.

C. Hydrolysis by hepatic carboxylesterase 1 after OATP1B1 uptake into hepatocytes — Enalapril is a prodrug: OATP1B1 transports it into hepatocytes, where carboxylesterase 1 hydrolyzes it to enalaprilat, the active and more potent inhibitor, which peaks 3–4 hours after an oral dose. Most ACE inhibitors are activated this way by hepatic esterases; lisinopril and captopril need no activation. The kidney excretes enalaprilat rather than activating it.

B. Reduced fetal glomerular filtration because fetal renal perfusion pressure depends on angiotensin II — The fetal kidney works at low pressure and depends on angiotensin II. RAS blockade in the second and third trimesters lowers fetal renal pressure and GFR, causing oligohydramnios and anuria, with risks of renal tubular dysplasia, lung and skull hypoplasia, renal failure and death. Oligohydramnios means less fetal urine, not polyuria. ACE inhibitors lower aldosterone rather than raise it, and their mechanism is ACE inhibition, not β blockade.

C. Switch to losartan (an ARB) — ACE-inhibitor cough comes from bradykinin, substance P and prostaglandins that build up because kininase II is inhibited. Every ACE inhibitor does this, so switching within the class does not help. ARBs do not inhibit kininase II or raise bradykinin, so their cough rate is 1–4% and cross-reactivity is under 3%. Dual RAS blockade — an ARB or aliskiren added to an ACE inhibitor — increases hyperkalemia, hypotension and renal dysfunction without added benefit, and aliskiren with an ACE inhibitor is contraindicated in diabetes.

D. It blocks the AT1 receptor without inhibiting ACE, so bradykinin does not accumulate — ACE is also kininase II, the enzyme that degrades bradykinin. Losartan does not inhibit ACE and does not affect the response to bradykinin, whereas ACE inhibitors increase it — so cough and angioedema are less common with ARBs. Angiotensin II synthesis is not reduced: renin and angiotensin II actually rise on an ARB. Neprilysin inhibition belongs to sacubitril, AT2 activation produces vasodilation partly through bradykinin rather than degrading it, and blocking bradykinin receptors is not losartan’s action — the labels say it does not affect the response to bradykinin.

B. Loss of angiotensin II negative feedback on renin secretion because AT1 is blocked — Blocking AT1 removes angiotensin II’s negative feedback on renin, so plasma renin rises two- to threefold and angiotensin II rises with it. The extra angiotensin II does not overcome the blockade, so blood pressure still falls, and it may stimulate the unblocked AT2 receptor. ARBs show no partial agonism at AT1, and aldosterone falls rather than rises.

E. Olmesartan — Olmesartan is associated with sprue-like enteropathy: severe chronic diarrhea with substantial weight loss, starting months to years after initiation, with villous atrophy on biopsy. Once other causes are excluded, the label advises considering an alternative antihypertensive.

C. Losartan — inhibits URAT1 in the proximal tubule — Among ARBs, losartan has uric acid–lowering properties: it acts as a uricosuric agent by inhibiting urate transporter 1 (URAT1) in the proximal tubule. Valsartan and candesartan had no notable effect on uric acid in their label studies.

A. Vasopressin — V1a-receptor vasoconstriction — ARB overdose causes vasodilatory (vasoplegic) shock with a high cardiac index, low vascular resistance and preserved cardiac function, and olmesartan’s long half-life can keep it going beyond 16 hours. In a reported case like this, catecholamines helped little (StatPearls attributes this to suppression of the sympathetic nervous system) and calcium-channel-blocker therapies failed, while vasopressin raised mean arterial pressure through V1a-receptor vasoconstriction. Drugs aimed at contractility do not target the low vascular resistance.

C. Inhibition of NKCC1 and ischemia in the cochlear stria vascularis — Loop ototoxicity comes from NKCC1 inhibition and ischemia in the stria vascularis, the cochlear tissue that secretes endolymph. It tracks serum concentration, so large IV boluses — especially in AKI — carry the most risk, and aminoglycosides and renal impairment add to it. It is usually reversible. Macula densa NKCC2 blockade turns off tubuloglomerular feedback, and aldosterone-driven potassium loss causes hypokalemia; neither affects hearing. NCC and ENaC are the thiazide and potassium-sparing targets, and ototoxicity is not shared by any other diuretic class.

A. Increased distal sodium delivery and aldosterone, trapping K⁺ and H⁺ in a lumen-negative distal tubule — Loops deliver more sodium distally and cause volume depletion, both of which activate the RAAS. Aldosterone drives avid sodium reabsorption, the lumen turns negative, and K⁺ and H⁺ are trapped and lost — hypokalemia with metabolic alkalosis, more common with loops than thiazides, with contraction alkalosis adding to it. Carbonic anhydrase inhibition (acetazolamide) causes metabolic acidosis, and ENaC blockade causes hyperkalemia and acidosis. Losing the lumen-positive voltage explains calcium and magnesium loss, not this pattern. Loops abolish the concentrating gradient rather than promoting free-water retention.

E. Na⁺-K⁺-2Cl⁻ cotransporter (NKCC2) of the thick ascending limb — NKCC2 loss of function causes type I Bartter syndrome, usually present at birth, with hypokalemic metabolic alkalosis, hypomagnesemia and nephrocalcinosis — the picture of a permanent loop diuretic, since losing the lumen-positive voltage lets calcium escape into the urine. Loss of NCC causes Gitelman syndrome, which shares the hypokalemic alkalosis and hypomagnesemia but features hypocalciuria. ENaC blockade causes hyperkalemia. NHE3 works in the proximal tubule, and aquaporin-2 is the vasopressin-regulated water channel of the collecting duct.

B. It removes the lumen-positive voltage in the thick ascending limb that drives paracellular calcium reabsorption — NKCC2 blockade stops ROMK from recycling potassium into the lumen, so the lumen-positive voltage falls and the paracellular drive for Ca²⁺ (and Mg²⁺) reabsorption is lost — calciuresis. NCC blockade is the thiazide mechanism, and thiazides promote calcium reabsorption. The furosemide label says its distal action is independent of carbonic anhydrase. Tubuloglomerular feedback normally lowers GFR by constricting the afferent arteriole, and loops inhibit it. The lumen-positive voltage is lost, not strengthened.

D. Ethacrynic acid — Ethacrynic acid is the only loop diuretic without a sulfonamide group, which makes it the safer choice when a sulfonamide allergy is a concern. Furosemide (a sulfamoylanthranilic acid), bumetanide (a sulfamoylbenzoic acid) and torsemide (a pyridine-sulfonylurea) all carry one, and thiazides are also sulfonamide derivatives. The trade-off: ethacrynic acid is the most ototoxic loop.

C. Thiazides impair urine dilution in the DCT while leaving the medullary concentrating mechanism intact — Loops actually block far more sodium reabsorption, yet hyponatremia is commoner with thiazides: they reduce free-water clearance by blocking the terminal diluting segment while the countercurrent concentrating mechanism stays intact. Higher water intake and vasopressin secretion add to the dilution, and the problem usually appears in the first 2–3 weeks of therapy.

B. By increasing tubular calcium reabsorption, proximally with volume depletion and possibly distally after NCC blockade — Thiazides increase calcium reabsorption: volume depletion boosts proximal sodium reabsorption, which carries calcium paracellularly, and NCC blockade may enhance distal reabsorption through TRPV5. Urinary calcium can fall by up to 50%, an effect StatPearls attributes to increased renal tubular calcium reabsorption. Potassium citrate is added because thiazides also lower serum potassium and urinary citrate. NKCC2 is the loop-diuretic target, and loops cause calciuresis.

A. Hydrochlorothiazide — This is Gitelman syndrome — loss of function of NCC, the thiazide target — with hypokalemic metabolic alkalosis, hypomagnesemia, hypocalciuria and lower blood pressure. A thiazide reproduces it pharmacologically. Furosemide is excluded by the low urinary calcium, because loop diuretics cause calciuresis. Spironolactone produces the opposite pattern — potassium-sparing diuretics cause hyperkalemia and a hyperchloremic metabolic acidosis — and acetazolamide, a carbonic anhydrase inhibitor, also causes a hyperchloremic metabolic acidosis rather than an alkalosis. Mannitol is an osmotic diuretic that does not interfere with electrolyte reabsorptive mechanisms, so it mimics no transporter defect.

E. Low potassium hyperpolarizes β-cells, keeping voltage-gated calcium channels closed and reducing insulin release — Thiazide-induced hypokalemia hyperpolarizes pancreatic β-cells: potassium channels stay open, voltage-gated calcium channels fail to open, and too little calcium enters to trigger insulin exocytosis. Reduced insulin sensitivity also contributes.

D. Metolazone blocks the compensatory distal sodium reabsorption that blunts the loop diuretic — Adding a thiazide-like drug to a loop diuretic interferes with compensatory distal tubular sodium reabsorption, increasing natriuresis, and metolazone can work even when GFR is below 20 mL/min. Metolazone does not inhibit carbonic anhydrase. Watch for hypokalemia, hyponatremia and worsening renal function.

D. Switch spironolactone to eplerenone — Spironolactone also binds androgen and progesterone receptors, causing dose-dependent, usually reversible gynecomastia — about 9% of men in RALES. Eplerenone blocks the same mineralocorticoid receptor but has 100–1000-fold lower affinity for these off-target receptors: gynecomastia was no more common than with placebo, and it has reversed spironolactone gynecomastia. Amiloride and triamterene block ENaC rather than the receptor, so they do not provide aldosterone blockade, and raising the spironolactone dose increases the gynecomastia risk. Stopping lisinopril would not help: aldosterone escapes ACE-inhibitor suppression, which is why the antagonist was added.

B. Amiloride — In Liddle syndrome, ENaC gain-of-function mutations (β or γ subunit) raise channel activity independently of aldosterone. The extra sodium reabsorption expands volume and suppresses renin and aldosterone, while potassium is secreted. Amiloride blocks ENaC directly and works even without aldosterone, so it treats Liddle syndrome. Liddle syndrome does not respond to aldosterone antagonism, so spironolactone and eplerenone, which act at the mineralocorticoid receptor, are not the answer. Furosemide acts on NKCC2 in the loop of Henle, and lisinopril on angiotensin II production — neither touches ENaC.

A. IV calcium, because it stabilizes the cardiac membrane — Calcium comes first in hyperkalemia with ECG changes because it stabilizes cardiac membranes. It does not lower serum potassium; potassium is then shifted into cells and removed. Peaked T waves followed by loss of P waves track rising potassium. Amiloride blocks ENaC and reduces K⁺ and H⁺ secretion, so the expected acid–base change is a hyperchloremic metabolic acidosis, not alkalosis. Spironolactone and triamterene are themselves potassium-sparing and would worsen the hyperkalemia; renal impairment, diabetes and an ARB all add to the risk.

E. Ritonavir, a strong CYP3A inhibitor, raises eplerenone levels and hyperkalemia risk; the combination is contraindicated — Eplerenone is cleared predominantly by CYP3A4, and the label contraindicates strong CYP3A inhibitors such as ritonavir, ketoconazole and clarithromycin. Higher levels raise hyperkalemia risk. Ritonavir inhibits CYP3A rather than inducing it. Eplerenone is not removed by hemodialysis, has no active metabolites, and its selectivity for the mineralocorticoid receptor is what spares the androgen receptor.

C. Spironolactone, because it competes with the aldosterone driving secondary aldosteronism — Ascites in cirrhosis involves secondary aldosteronism. By competing with aldosterone for its receptor, spironolactone treats the edema and ascites, and StatPearls calls it the drug of choice for initial therapy, with a loop added as an adjunct or from the outset — so a loop alone is not the usual first step. Amiloride is not an aldosterone antagonist; it blocks ENaC. Spironolactone, not eplerenone, is the named drug of choice to start in cirrhotic ascites. Thiazides act on NCC and do not address the aldosterone excess.

C. Precapillary arteriolar dilation raising capillary hydrostatic pressure — Dihydropyridines preferentially dilate precapillary arterioles, raising intracapillary hydrostatic pressure and transcapillary filtration. The edema is not fluid retention and does not respond to diuretics, which is why furosemide did not help. An ACE inhibitor or ARB attenuates it by dilating postcapillary venules. Amlodipine has not been associated with a negative inotropic effect in the therapeutic range, and her normal venous pressure and albumin argue against heart failure and hypoalbuminemia.

E. Diltiazem, because it slows calcium-dependent AV-node conduction — AV-node conduction depends on calcium influx, and diltiazem (like verapamil) binds the open channel in nodal tissue, slowing AV conduction and controlling the ventricular rate in atrial fibrillation. The dihydropyridines — amlodipine, nifedipine, clevidipine and nicardipine — are vessel-selective with little effect on pacemaker or nodal tissue; clevidipine does not reduce heart rate, and their vasodilation can even raise it reflexly. Diltiazem would be avoided with heart failure with reduced EF or an accessory pathway.

A. Blocked L-type channels in pancreatic β cells reduce insulin release — Pancreatic β cells depend on calcium influx through L-type channels to release insulin, so CCB overdose reduces insulin secretion and promotes insulin resistance; the hyperglycemia is a marker of severity, especially with nondihydropyridines. The verapamil label also lists hyperglycemia among overdose effects secondary to hypoperfusion — an indirect effect, whereas the drug’s own action is on the β cell. The same energy failure in the heart is why high-dose insulin with glucose improves contractility. Verapamil inhibits L-type voltage-gated calcium channels rather than opening β-cell ATP-sensitive K⁺ channels, and skeletal muscle depends mainly on intracellular calcium stores rather than calcium influx; its CYP3A4 and P-glycoprotein inhibition raises levels of other drugs such as statins, cyclosporine and digoxin rather than driving gluconeogenesis. Her bradycardia and hypotension reflect nodal suppression, vasodilation and reduced contractility; IV calcium, vasopressors and high-dose insulin are the mainstays, and whole-bowel irrigation is considered for an extended-release ingestion.

D. Nicardipine inhibits hepatic CYP3A4, which metabolizes tacrolimus — Oral or IV nicardipine raises tacrolimus (and cyclosporine) levels by inhibiting hepatic microsomal enzymes, including CYP3A4, so trough levels need close monitoring. Clevidipine, cleared by esterases with no CYP inhibition or induction, is the IV dihydropyridine without this interaction. Protein displacement, a lower GFR or P-glycoprotein induction is not the mechanism the label describes.

B. It slows the AV node but may shorten the accessory pathway’s refractory period, letting more impulses reach the ventricles — Verapamil prolongs the AV-node refractory period but may shorten the antegrade refractory period of an accessory bypass tract. With the node slowed, impulses run down the accessory pathway, and IV verapamil has produced a very rapid ventricular response or ventricular fibrillation — so the label contraindicates it in atrial fibrillation or flutter with an accessory pathway. Verapamil acts strongly on the heart, not mainly on vessels, and it clearly slows AV conduction; reflex tachycardia is a dihydropyridine effect.

E. Cyanide binding cytochrome c oxidase and blocking oxidative phosphorylation — Nitroprusside reacts with hemoglobin to release cyanide; once methemoglobin buffering and thiosulfate-dependent conversion to thiocyanate are overwhelmed, free cyanide binds cytochrome c oxidase. Cells switch to anaerobic metabolism (lactic acidosis) and cannot extract oxygen, so venous blood stays oxygen-rich. Thiocyanate toxicity is slower (days, renal failure) and presents with tinnitus and confusion; methemoglobinemia needs very large amounts.

B. Slow (poor-metabolizer) NAT2 acetylator status — Hydralazine undergoes polymorphic acetylation. Slow acetylators (NAT2 poor metabolizers) have higher hydralazine levels and are predicted by CPIC to have more adverse effects, including drug-induced lupus; female sex and cumulative exposure add risk. Antihistone antibodies are present in more than 95% of hydralazine-induced cases, while anti-dsDNA is usually absent.

D. Loss of central alpha-2 suppression of sympathetic outflow, with a catecholamine surge — Clonidine lowers BP by stimulating brainstem alpha-2 receptors and reducing sympathetic outflow. Abrupt withdrawal releases that brake: nervousness, agitation, headache and tremor with a rapid BP rise and high plasma catecholamines. The risk is greater when a beta-blocker is involved, which is why the beta-blocker is withdrawn several days before clonidine is tapered.

A. IgG coating of her red cells induced by methyldopa — With prolonged methyldopa therapy, 10–20% of patients develop a positive direct Coombs test as the red cells become coated with IgG. Without hemolytic anemia, usually only the direct test is positive, which does not interfere with typing or cross-matching; both direct and indirect tests are done before transfusion. Methyldopa’s fluorescence interferes with urinary catecholamine tests, not the Coombs test.

C. A beta-blocker and a loop diuretic, to blunt reflex tachycardia and renin-driven salt and water retention — Minoxidil opens K-ATP channels and lowers peripheral resistance, which triggers sympathetic, vagal-inhibitory and renal homeostatic responses: faster heart rate and output, more renin and salt and water retention. The label requires a beta-blocker (or other sympathetic suppressant) and usually a loop diuretic. Minoxidil itself does not cause orthostatic hypotension. Without a diuretic it retains several hundred milliequivalents of salt, with the matching water, within a few days, so a beta-blocker alone is not enough. Its hypertrichosis has no endocrine explanation and stops only when minoxidil is discontinued, so an ACE inhibitor would not prevent it, and sympathomimetics such as epinephrine are avoided because of their excessive cardiac stimulation.

E. Pregnancy test — Ambrisentan, like all ERAs and riociguat, carries a boxed warning for embryo-fetal toxicity: pregnancy is excluded before starting, contraception is used before, during and for one month after treatment, and the drug is stopped when pregnancy is detected. Monthly aminotransferase monitoring belongs to bosentan’s hepatotoxicity box; ambrisentan has no hepatotoxicity warning (ALT/AST > 3× ULN in 0% vs 2.3% on placebo). At usual doses, without metabolic inhibitors, ambrisentan is not expected to prolong the QT interval significantly, and mild or moderate renal impairment needs no dose adjustment — so neither an ECG nor a serum creatinine is a prerequisite.

C. Nitroglycerin increases cGMP formation while tadalafil blocks its breakdown, causing profound hypotension — Nitrates increase cGMP formation and PDE-5 inhibitors block cGMP degradation, so together they cause severe hypotension; the tadalafil labels say not to use nitrates within 48 hours of the last dose, and tadalafil’s half-life is about 35 hours in pulmonary hypertension. Tadalafil is itself a CYP3A substrate — the danger is pharmacodynamic, through the shared NO–cGMP pathway — and neither drug blocks sGC.

A. Rebound pulmonary hypertension after interruption of a drug with a half-life of minutes — Epoprostenol’s in vivo half-life is no more than about 6 minutes, so an interruption removes it almost at once; abrupt withdrawal causes rebound pulmonary hypertension with dyspnea, dizziness and asthenia, and a death has been attributed to an interruption — hence the backup pump. Overdose would instead look like excess vasodilation — flushing, headache, hypotension, tachycardia.

D. Sensitizes soluble guanylate cyclase to nitric oxide and stimulates it directly, independent of nitric oxide — Riociguat is the sGC stimulator labelled for persistent or recurrent CTEPH after surgery or inoperable CTEPH. It stabilizes NO–sGC binding and also stimulates sGC at a separate site without NO. Its active metabolite is formed by CYP1A1, which cigarette smoke induces, so levels are 50–60% lower in smokers and a dose decrease may be needed after quitting. PDE-5 inhibitors only slow cGMP breakdown, and riociguat is contraindicated with them.

B. Nitroglycerin raises cGMP synthesis while sildenafil blocks its breakdown — Nitrates release NO, which activates soluble guanylate cyclase to make cGMP; phosphodiesterases end the signal by hydrolyzing cGMP to GMP. A PDE5 inhibitor blocks that breakdown, so vasodilation is potentiated, and the labels warn that the combination can cause severe hypotension, syncope or myocardial ischemia. Nitroglycerin’s part is the nitric oxide — ALDH2 bioactivates it — while sildenafil is the PDE-5 inhibitor, so blocking ALDH2 would weaken nitroglycerin rather than deepen its effect. Nitroglycerin’s venous effects predominate (hydralazine is the selective arterial dilator), and ordinary doses of organic nitrates cause methemoglobinemia only extremely rarely.

E. Nitrate tolerance — remove the patch for a daily 10–12-hour drug-free interval — Continuously delivered nitrates are no better than placebo after 24 hours or less, and dose escalation consistently fails; efficacy returns only after nitrates have been absent for several hours. For nitroglycerin, a daily drug-free interval of 10–12 hours is usually sufficient.

D. Calcium-channel blocker — This is coronary vasospasm (Prinzmetal angina): rest pain at night or early morning with ECG changes that resolve on a fast-acting nitrate. Calcium antagonists are first-line because of their coronary vasodilatory effect; sublingual nitrates relieve attacks and long-acting nitrates are added when the response is incomplete. β-blockers, particularly nonselective ones, are avoided because they can worsen the symptoms.

C. Nitrate ions oxidized hemoglobin to the ferric (Fe³⁺) state — give methylene blue — Nitrate ions released during metabolism oxidize hemoglobin iron from Fe²⁺ to Fe³⁺, and ferric hemoglobin cannot bind oxygen. Hypoxemia despite a normal arterial PO₂ and chocolate-brown blood that does not redden in air point to methemoglobinemia; methylene blue is the antidote.

A. It is not subject to first-pass hepatic metabolism — Isosorbide dinitrate undergoes extensive first-pass hepatic metabolism, so its bioavailability ranges from 10% to 90% (about 25% on average). Isosorbide mononitrate, its major active metabolite, is not subject to first-pass metabolism and has an absolute bioavailability of about 100%; it is only about 5% protein-bound, and only about 2% of a dose is excreted unchanged.

B. Inhibition of the late sodium current, reducing calcium overload in ischemic myocytes — Ranolazine inhibits the late inward sodium current in ischemic myocytes, lowering intracellular sodium and calcium influx through the Na⁺–Ca²⁺ exchanger, which reduces wall tension and oxygen consumption without significantly affecting heart rate or blood pressure. Beta-blockers, calcium channel blockers and nitrates lower oxygen demand by slowing the heart, reducing contractility or dilating vessels, and this patient’s heart rate and blood pressure are already low.

A. Clarithromycin, a strong CYP3A inhibitor, raised ranolazine levels and its IKr-mediated QT effect — Ranolazine is metabolized mainly by CYP3A; strong CYP3A inhibitors such as clarithromycin are contraindicated (ketoconazole raised ranolazine levels by 220%). The QTc rises linearly with ranolazine plasma concentration because of IKr block. Clarithromycin is an inhibitor, not an inducer, and ranolazine’s OCT2 inhibition affects drugs such as metformin.

D. It inhibits the excess late sodium current that prolongs the action potential in LQT3 — Long QT syndrome type 3 results from gain-of-function mutations that increase late inward sodium current. Ranolazine inhibits that current, shortening the abnormally prolonged QTc; in other patients its IKr block is what prolongs the QT, while late sodium inhibition shortens or barely changes action potential duration. Beta-blockers slow the heart and non-dihydropyridine calcium-channel blockers inhibit the SA and AV nodes, but ranolazine’s antianginal effects do not depend on lowering heart rate or blood pressure — mean heart rate changes by less than 2 bpm and systolic pressure by less than 3 mm Hg — so neither nodal block nor a faster rate explains the shorter QTc.

E. Inhibition of tubular creatinine secretion — benign and reversible — Ranolazine raises serum creatinine by about 0.1 mg/dL regardless of renal function, likely by inhibiting tubular creatinine secretion; the rise is rapid, does not progress, reverses on stopping and is not accompanied by a change in BUN, and ranolazine had no effect on glomerular filtration rate in healthy volunteers. A marked, progressive rise with rising BUN or potassium would instead suggest acute renal failure, reported in severe renal impairment.

E. Na⁺/K⁺-ATPase inhibition raises intracellular Na⁺, so the Na⁺/Ca²⁺ exchanger leaves more Ca²⁺ in the cell — All of digoxin’s actions are mediated through the Na⁺/K⁺-ATPase. Reversibly inhibiting it raises intracellular sodium, which reduces exchange through the Na⁺/Ca²⁺ exchanger, so calcium accumulates in the myocyte and increases contractility. The vagal effect slows the SA and AV nodes rather than strengthening contraction.

B. The assay measures digoxin that is now bound to Fab and inactive — After Fab, total serum digoxin may rise precipitously, but it is almost entirely Fab-bound and unable to reach its receptors; standard digoxin assays stay clinically misleading until the Fab is eliminated. That is why the level should be drawn before Fab is given.

A. Amiodarone inhibits P-glycoprotein, reducing digoxin’s renal tubular secretion — Digoxin is a P-glycoprotein substrate in intestinal absorption, renal tubular secretion and biliary secretion; in vitro, amiodarone inhibits renal P-glycoprotein transport, which can reduce digoxin clearance (the label lists a 70% rise in serum digoxin). Digoxin is not metabolized by cytochrome P450 and is only about 25% protein-bound.

C. Inhibition of the Na⁺/K⁺-ATPase shifts potassium out of cells — Digoxin causes a shift of potassium from inside to outside the cell, so severe intoxication can produce life-threatening hyperkalemia; it is the major electrolyte complication of acute toxicity and a marker of severity, and hyperkalemia is an indication for digoxin Fab.

D. Its AV slowing is largely vagally mediated, and it does not significantly reduce heart rate during exercise — Digoxin slows the AV node through indirect parasympathetic stimulation, and the label limits its atrial fibrillation indication to control of the resting rate, noting that digoxin does not significantly reduce heart rate during exercise. Its half-life is 1.5–2 days, so it does not wear off within hours. All of digoxin’s actions are mediated through the Na-K ATPase, not β1 receptors; it increases the refractory period rather than shortening it; and only about 13% of a dose is metabolized, with 50–70% excreted unchanged in the urine.

C. Ongoing urinary glucose loss while a high glucagon/insulin ratio drives ketogenesis — This is euglycemic diabetic ketoacidosis: glucose below 250 mg/dL with severe metabolic acidosis and ketonemia. Glucose keeps draining into the urine, insulin falls and glucagon rises (SGLT2 inhibitors also stimulate glucagon release), so lipolysis and ketogenesis run while blood glucose stays near normal; reduced intake and illness are typical triggers. The drug is stopped and the patient is treated with fluids and insulin plus dextrose. Metformin-associated lactic acidosis is not the explanation: ketones must be raised to make this diagnosis, and lactic acid may rise but should not account entirely for the anion gap.

B. Natriuresis that lowers preload, with reduced afterload and sympathetic activity — Dapagliflozin reduces sodium as well as glucose reabsorption, increasing distal sodium delivery; the labels link this to lower cardiac preload and afterload and downregulated sympathetic activity, and natriuresis and diuresis reduce preload. Its heart-failure indication — reducing cardiovascular death and heart-failure hospitalization — applies with or without diabetes. Dapagliflozin works by inhibiting SGLT2 in the proximal tubule — it is not an insulin secretagogue, a β1 agonist, a mineralocorticoid-receptor blocker or an inhibitor of gluconeogenesis — and its hypoglycemia risk arises mainly when it is combined with insulin or an insulin secretagogue.

A. SGLT2 — Isolated glucosuria with normal plasma glucose points to familial renal glucosuria, caused by an SGLT2 mutation; SGLT2 performs more than 90% of proximal glucose reabsorption. An SGLT1 mutation causes glucose-galactose malabsorption, a GLUT2 mutation Fanconi-Bickel syndrome, and Fanconi syndrome adds phosphaturia, aminoaciduria and acidosis.

D. Stop dapagliflozin and arrange urgent surgical evaluation with broad-spectrum antibiotics — Pain out of proportion to the findings in the perineum with fever suggests Fournier’s gangrene, a necrotizing fasciitis linked to SGLT2 inhibitors. The labels say to evaluate immediately and, if it is suspected, to discontinue the drug and institute prompt medical and surgical treatment; time to surgery is the most important factor in mortality, which is about 40%. Raising the dose, waiting a week or applying a topical antibiotic would each delay that evaluation, discontinuation and surgery.

B. Accumulation of bradykinin from combined neprilysin and ACE inhibition — Neprilysin and ACE both break down bradykinin. Starting sacubitril/valsartan before the ACE inhibitor has cleared lets bradykinin accumulate and causes angioedema — which is why the combination is contraindicated and a 36-hour gap is required. Valsartan blocks the AT1 receptor, so angiotensin II is not left acting there; sacubitril is a prodrug whose esterase product, LBQ657, works by inhibiting neprilysin; and natriuretic peptides cause diuresis and inhibit sodium and water reabsorption rather than retaining salt.

C. BNP is a neprilysin substrate, so it rises on the drug; NT-proBNP is the reliable marker — ProBNP is split into BNP and NT-proBNP. Neprilysin degrades BNP but not NT-proBNP, so neprilysin inhibition raises BNP independently of heart-failure status, while NT-proBNP reflects the disease — her symptoms need clinical assessment, but the BNP rise is expected.

C. Partial inhibition of the retinal Ih current — Ivabradine blocks the cardiac If current and partly blocks the related retinal Ih current, which normally curtails responses to bright light. Sudden changes in luminosity then produce phosphenes — usually in the first 2 months, mild, and mostly resolving. The label ties them to ivabradine’s effects on retinal photoreceptors and to sudden variations in light intensity, and in dogs its retinal changes reversed within a week without damage to ocular structures — a reversible current effect, not ischemic, inflammatory or lens damage. He takes carvedilol, not digoxin.

B. Both raise cGMP signaling, adding to hypotension — Vericiguat stimulates sGC to make more cGMP, and PDE-5 inhibitors prevent cGMP breakdown. Together they deepen vasodilation, so the label does not recommend the combination; another sGC stimulator is contraindicated. Sildenafil enhances cGMP signaling by inhibiting cGMP-specific phosphodiesterases — it does not donate nitric oxide or block If, ivabradine’s target. The problem is pharmacodynamic: sildenafil does not change vericiguat’s pharmacokinetics, vericiguat does not change sildenafil’s, and vericiguat does not inhibit CYP3A4.

D. Slow acetylator phenotype — Procainamide is acetylated to NAPA, and its lupus-like syndrome — positive ANA with arthralgia, pleuritis, fever — is fairly common with prolonged use and perhaps more frequent in slow acetylators. It usually resolves when the drug is stopped. CYP2D6 status matters for propafenone, and dietary salt alters quinidine levels, not procainamide toxicity.

A. A drug-dependent antibody that binds platelet glycoproteins only in the presence of quinidine — Quinidine-induced thrombocytopenia is immune-mediated: a drug-dependent antibody, nonreactive by itself, binds tightly to platelet membrane glycoproteins when quinidine is present and destroys platelets. It typically appears after about a week of therapy as petechiae or bruising. Quinidine is stopped at once — the count usually recovers within a week — and the patient must not be re-exposed.

C. Adding a β-blocker — Flecainide can convert atrial fibrillation to atrial flutter with 1:1 conduction, so a β-blocker or calcium channel blocker is given with it to slow AV-node conduction. The flecainide label names digoxin or β-blockers for this, and advises that verapamil, a negative inotrope, not be given with flecainide unless the benefits outweigh the risks; there is too little experience with diltiazem to recommend it. Its strong, slowly dissociating sodium block also widens the QRS, especially at fast rates (use dependence). Class Ic drugs are reasonable only in hearts without structural or ischemic disease. A second class Ic drug or a higher dose would only add sodium-channel block — flecainide’s PR, QRS and QT increases are dose-related, and serious adverse events become more frequent at higher trough levels; food does not affect its absorption; and diuretic use and hypokalemia are risk factors for torsades, which is why hypokalemia is corrected before flecainide is given.

E. IV magnesium — This is torsades de pointes from potassium-channel block: sotalol prolongs repolarization, and its reverse use dependence makes it worse at slow rates; hypokalemia and diuretic use add risk. IV magnesium is the first-line drug, with stopping QT-prolonging drugs and correcting potassium. Procainamide (Ia) and amiodarone (III) prolong the QT further; adenosine restores sinus rhythm in PSVT, not torsades. Isoproterenol is used for runs that persist despite magnesium. Lidocaine is not the first-line drug for torsades — magnesium is.

B. Procainamide, because potent sodium-channel block can unmask the Brugada pattern — Brugada syndrome is most often a loss-of-function mutation in SCN5A, the cardiac sodium channel. Potent sodium blockers — procainamide, flecainide, ajmaline — can convert a non-diagnostic pattern to the diagnostic type 1 pattern. Quinidine, by contrast, is used to treat Brugada electrical storm. Lidocaine is a weak (Ib) sodium blocker; adenosine, sotalol and verapamil act on other targets.

E. SREBP-driven increase in hepatocyte LDL receptors — Lower intracellular cholesterol activates SREBP, which moves from the ER to the Golgi, is cleaved and enters the nucleus to increase LDL-receptor expression. More hepatic LDL receptors take up LDL from the blood — LDL receptors on the liver determine plasma LDL.

D. CYP3A4 inhibition raised simvastatin exposure — Simvastatin is a CYP3A4 substrate; strong CYP3A4 inhibitors such as clarithromycin increase simvastatin exposure and the risk of myopathy and rhabdomyolysis, which is why they are contraindicated together. Myopathy risk rises with the plasma level of HMG-CoA reductase inhibitory activity. Immune-mediated necrotizing myopathy is different: a rare autoimmune myopathy associated with statin use itself, with anti-HMG-CoA reductase antibodies and weakness that persists after the statin is stopped.

A. Rosuvastatin — Rosuvastatin clearance does not depend on CYP3A4 to a clinically significant extent (about 10% is metabolised, mainly by CYP2C9). Simvastatin and lovastatin are contraindicated with strong CYP3A4 inhibitors such as HIV protease inhibitors, and atorvastatin levels rise. Transporter interactions still need checking.

C. SLCO1B1 — reduced hepatic uptake and higher simvastatin acid exposure — SLCO1B1 encodes OATP1B1. Poor function raises simvastatin acid exposure and highly increases myopathy risk; CPIC (level A) recommends an alternative statin. ABCG2 matters for rosuvastatin.

B. Absent functional LDL receptors, so statin-induced receptor upregulation cannot occur — A homozygous LDL-receptor mutation leaves no receptors on hepatocytes, raising LDL to around 1000 mg/dL. Statins lower LDL mainly by upregulating LDL receptors, so the lovastatin label notes reduced effectiveness in homozygous familial hypercholesterolemia, possibly because these patients have no functional LDL receptors. Statins still competitively inhibit HMG-CoA reductase, but the receptor upregulation that follows has no receptors to act on — so the problem lies in the LDL receptor named in the stem, not in statin absorption, metabolism, enzyme binding or antibodies.

D. Increased PCSK9 activity — Statins lower intracellular cholesterol and increase LDL-receptor expression, but they also increase PCSK9 activity, which diminishes their efficacy. A PCSK9 antibody such as evolocumab or alirocumab blocks PCSK9 binding to the LDL receptor, so more receptors recycle and clear LDL; LDL-C typically falls 50–60% with or without a statin.

C. No functional LDL receptors for the drug to preserve — PCSK9 antibodies lower LDL-C by increasing the number of LDL receptors available to clear LDL. Patients with two LDL-receptor-negative alleles (little or no residual function) did not respond to evolocumab in the HoFH trial. Monoclonal antibodies are not known to be renally eliminated, and only 0.3% of evolocumab patients developed binding antibodies, none neutralizing.

B. PCSK9, gain of function — Gain-of-function PCSK9 mutations cause autosomal dominant familial hypercholesterolemia — high LDL-C, premature atherosclerosis and tendon xanthomas — and were first found in a family without LDL-receptor or apoB100 mutations. PCSK9 loss of function does the opposite: lower LDL-C and less coronary heart disease.

E. Her drug is a PCSK9 antibody that binds circulating PCSK9; her friend’s is an siRNA that blocks PCSK9 synthesis inside liver cells — Evolocumab and alirocumab are monoclonal antibodies that bind PCSK9 and stop it binding the LDL receptor, given subcutaneously every 2 to 4 weeks. Inclisiran is a small interfering RNA that inhibits intracellular PCSK9 synthesis, given initially, at 3 months and then every 6 months.

B. Gemfibrozil inhibits OATP1B1, raising statin exposure on top of the fibrate’s own myopathy risk — Fibrates can cause myopathy alone, and the risk rises with statins. Gemfibrozil also inhibits OATP1B1, a hepatic transporter of simvastatin and other statins, so statin exposure increases — which is why gemfibrozil with simvastatin is contraindicated and the combination has led to rhabdomyolysis and acute renal failure. Fenofibrate, by contrast, changes statin exposure only modestly. Fibrates are metabolized mainly by glucuronidation, and their lipid effects — activating PPAR-α, increasing lipoprotein lipase and lowering apo C — clear triglyceride-rich lipoproteins; what makes this case severe is the OATP1B1 interaction on top of the fibrate’s own myopathy risk.

D. A recognized effect: treating Type IV hypertriglyceridemia with gemfibrozil often raises LDL-cholesterol — Gemfibrozil lowers triglycerides and VLDL, but its label notes that treating elevated triglycerides due to Type IV hyperlipoproteinemia often results in a rise in LDL-cholesterol. Gemfibrozil acts through PPAR-α, inhibits peripheral lipolysis and decreases hepatic VLDL apoB production; it does not act on LDL receptors or HMG-CoA reductase, and hypothyroidism is a secondary cause of high triglycerides to look for before treatment, not an effect of the drug.

A. Increased cholesterol excretion into bile — Fibrates may increase cholesterol excretion into bile, leading to cholelithiasis. The fibrate is stopped when gallstones are found, and pre-existing gallbladder disease is a contraindication. CYP2C8 inhibition is not the link: fenofibrate is only a weak CYP2C8 inhibitor, and the CYP2C8 inhibitor that matters for interactions such as repaglinide is gemfibrozil.

E. It raises repaglinide exposure about 8-fold through CYP2C8 and OATP1B1 inhibition, causing severe hypoglycemia — Gemfibrozil is a strong CYP2C8 inhibitor and an OATP1B1 inhibitor; repaglinide AUC rose 8.1-fold with prolonged hypoglycemic effects, so the combination is contraindicated. The problem is pharmacokinetic, not an action at repaglinide’s receptor; gemfibrozil’s lipid effects come from PPAR-α, not PPAR-γ; lactic acidosis is metformin’s boxed warning; and increased urinary glucose excretion is how SGLT2 inhibitors such as empagliflozin work.

C. Cholesterol 7-α-hydroxylase — Cholestyramine binds bile acids in the gut; as the bile-acid pool shrinks, cholesterol 7-α-hydroxylase — the rate-limiting step of bile-acid synthesis — is disinhibited, increasing conversion of cholesterol to bile acids. The resulting hepatic demand raises HMG-CoA reductase activity and LDL-receptor number, so LDL-C falls.

A. It can raise triglycerides, and it is contraindicated with triglycerides above 500 mg/dL — Colesevelam is labeled to lower LDL-C and to improve glycemic control in type 2 diabetes, but like other bile acid sequestrants it can increase triglycerides, and hypertriglyceridemia can cause acute pancreatitis; it is contraindicated with triglycerides above 500 mg/dL. It is not absorbed and does not interfere with CYP450 enzymes.

E. Chloride released from the chloride-form anion-exchange resin — Cholestyramine is the chloride form of an anion-exchange resin, and prolonged use may produce hyperchloremic acidosis, especially in younger and smaller patients in whom the relative dose is higher. Diarrheal bicarbonate loss does not fit either: no diarrhea is reported, and the resin’s most common adverse reaction is constipation.

D. The resin binds levothyroxine in the gut; give levothyroxine at least 1 hour before or 4–6 hours after cholestyramine — Cholestyramine can delay or reduce the absorption of thyroid and thyroxine preparations taken at the same time; other drugs are taken at least 1 hour before or 4–6 hours after the resin. The interaction is binding in the gut, not enzyme induction.

B. Prostaglandins released after GPR109A activation on epidermal Langerhans cells; blunted by aspirin beforehand — Niacin acts on GPR109A on epidermal Langerhans cells, activating prostaglandins that vasodilate the skin; aspirin taken beforehand reduces flushing. Switching to sustained-release niacin at the same dose risks severe hepatotoxicity.

C. Bempedoic acid — it inhibits the renal tubular transporter OAT2 — Bempedoic acid is activated by ACSVL1, present in liver but absent from muscle, and inhibits ACL. It inhibits renal OAT2, raising uric acid within the first weeks.

E. Abetalipoproteinemia (MTP deficiency) — Lomitapide inhibits microsomal triglyceride transfer protein, so apo B lipoproteins are not assembled — the defect of abetalipoproteinemia (MTTP mutations), with fat malabsorption and fat-soluble vitamin deficiency; in the liver the retained fat appears as steatosis.

A. It is an siRNA that directs catalytic breakdown of PCSK9 mRNA inside hepatocytes — Inclisiran, GalNAc-targeted to hepatocytes, uses RNA interference to break down PCSK9 mRNA; with a plasma half-life of about 9 hours, LDL-C is still about 53% lower at day 180. The antibodies, by contrast, bind PCSK9 and reduce free PCSK9 in the circulation.

B. IgG against heparin–PF4 complexes activates platelets through Fc receptors — In HIT, IgG binds the heparin–PF4 complex and engages platelet Fc receptors, activating platelets, which release more PF4 and procoagulants; the antibody-coated platelets are cleared, so the count falls while thrombosis rises. All heparin must stop, and a non-heparin anticoagulant such as argatroban, bivalirudin or fondaparinux is started. Fondaparinux binds antithrombin but not PF4 and does not react with HIT antibodies.

E. Protein C, with a short half-life, falls before factors II, IX and X, causing a transient hypercoagulable state — Warfarin blocks VKORC1, so all vitamin K-dependent proteins decline according to their half-lives: protein C (about 8 h) before factor II (60 h) and X (48–72 h). The resulting acquired protein C deficiency makes the first days prothrombotic, and inherited protein C or S deficiency raises the risk — the reason heparin overlaps warfarin at the start.

A. Idarucizumab — Idarucizumab is a humanized antibody fragment that binds dabigatran (and its metabolites) with higher affinity than dabigatran binds thrombin, neutralizing it. Dabigatran is mainly renally cleared, so reduced renal function prolongs its effect; hemodialysis can also remove it. Andexanet is labeled for apixaban and rivaroxaban, protamine for heparin, and vitamin K for warfarin.

D. Dabigatran is contraindicated with mechanical valves, and warfarin remains the anticoagulant for them — Dabigatran is contraindicated in patients with a mechanical prosthetic heart valve, and rivaroxaban, apixaban and edoxaban are not recommended with prosthetic or mechanical valves. Warfarin is used with valve-specific INR targets (for example 2.5–3.5 for a mechanical mitral valve).

C. Reduced CYP2C9 7-hydroxylation of the more potent S-warfarin — CYP2C9*2 and *3 reduce 7-hydroxylation of S-warfarin, so exposure rises and lower maintenance doses are needed; *3/*3 patients may take more than 2–4 weeks to reach the maximum INR for a given regimen. VKORC1 variants also lower dose needs, and CPIC has a level-A guideline for CYP2C9, VKORC1 and CYP4F2 with warfarin.

E. It irreversibly acetylates COX-1 in platelets, which cannot make new enzyme — Aspirin irreversibly inhibits platelet COX-1. Platelets cannot synthesise new COX, so thromboxane A₂ production stays suppressed for the platelet’s lifespan — about 7 to 10 days — long after the drug has been hydrolysed. Salicylate elimination is first-order at low doses.

C. Reduced conversion of clopidogrel to its active thiol metabolite — Clopidogrel is a prodrug; CYP2C19 participates in both oxidative steps to the active thiol metabolite. Poor metabolizers — more common in Asian patients — form less active metabolite and have less platelet inhibition, the subject of the boxed warning. CPIC recommends avoiding clopidogrel in poor metabolizers and using prasugrel or ticagrelor if not contraindicated. Aspirin is hydrolysed in plasma in everyone, but its COX-1 inhibition is irreversible, so that does not matter; COX-2 is found in only a small fraction of circulating platelets; clopidogrel’s active metabolite binds P2Y12 irreversibly, so its effect does not fade between doses; and clopidogrel is extensively metabolized — mostly by esterases to an inactive acid — rather than excreted unchanged.

D. Clopidogrel’s short-lived active metabolite could not bind P2Y12 while cangrelor occupied it — Clopidogrel or prasugrel given during a cangrelor infusion has no antiplatelet effect until the next dose, because cangrelor occupies P2Y12 while the thienopyridine’s short-lived active metabolite is present. They are given after the infusion stops; ticagrelor can be given during it. Cangrelor itself needs no metabolic activation and its pharmacokinetics do not depend on hepatic function; it is dephosphorylated to a nucleoside with negligible antiplatelet activity, not to an antagonist; and clopidogrel is activated by the cytochrome P450 system, not by the kidney.

A. As a PDE III inhibitor, it belongs to a drug group that has decreased survival in heart failure — Cilostazol and several of its metabolites inhibit phosphodiesterase III. Several drugs with this effect have decreased survival in class III–IV heart failure, so cilostazol carries a boxed contraindication in heart failure of any severity. It is metabolised by CYP3A4 and CYP2C19, not cleared unchanged. Cilostazol itself is active — it and several metabolites inhibit PDE III, raising cAMP and reversibly inhibiting aggregation — so it is not a prodrug, and irreversible P2Y12 blockade belongs to clopidogrel and prasugrel. It raises the heart rate by about 5–7 beats per minute rather than slowing it.

B. Stop both the GP IIb/IIIa inhibitor and heparin, and monitor platelet counts — GP IIb/IIIa inhibitors can cause acute, profound thrombocytopenia, immune-mediated or not. Once thrombocytopenia is confirmed (and pseudothrombocytopenia excluded), both the GP IIb/IIIa inhibitor and heparin are stopped and platelet counts are followed; counts usually recover after the drug is stopped. Every other choice keeps the GP IIb/IIIa infusion running — transfusing over it, replacing only the heparin, increasing the rate or adding aspirin — when the label calls for stopping it.

A. Bradykinin, generated with plasminogen activation and degraded more slowly with ACE inhibition — Orolingual angioedema with alteplase is linked to bradykinin: plasminogen activation feeds bradykinin synthesis (tranexamic acid limits it by interrupting that activation), and ACE inhibitors reduce bradykinin degradation. Many patients with alteplase angioedema were taking an ACE inhibitor. Bradykinin-mediated angioedema is distinct from histamine-mediated (allergic) angioedema and is not triggered by allergic reactions or hives. Alteplase acts by converting fibrin-bound plasminogen to plasmin; it does not inhibit cyclooxygenase or activate platelets, so leukotrienes, thromboxane A₂ and serotonin are not the link.

C. Cryoprecipitate — Plasmin generated by alteplase lyses fibrinogen as well as fibrin. Cryoprecipitate is commonly used to restore fibrinogen after symptomatic intracranial hemorrhage; an antifibrinolytic such as aminocaproic acid or tranexamic acid blocks further plasminogen activation and is considered when cryoprecipitate is delayed or unavailable, but it does not replace fibrinogen. Vitamin K is the antidote for warfarin, protamine reverses heparin, and idarucizumab reverses dabigatran.

D. Its longer plasma half-life — Tenecteplase has higher fibrin specificity, resistance to inactivation by PAI-1 and a longer half-life than native tPA; because of its long half-life it can be given as a single IV bolus (terminal half-life 90–130 minutes, versus an initial alteplase half-life under 5 minutes). It is not a prodrug — tenecteplase itself binds fibrin and converts plasminogen — and it is cleared mainly by liver metabolism; it resists PAI-1 rather than blocking its synthesis.

E. Alteplase remained active in the tube and degraded fibrinogen in vitro — At pharmacologic concentrations alteplase stays active in vitro and can degrade fibrinogen in blood removed for analysis, so coagulation tests and measures of fibrinolytic activity may be unreliable during therapy unless specific precautions are taken to prevent in vitro artifacts.

A. Verapamil — Verapamil is a class IV L-type calcium-channel blocker that slows SA-node pacing and AV-node conduction and lengthens the PR interval. Chronic verapamil can raise serum digoxin levels by 50% to 75% in the first week and cause digitalis toxicity; nausea, vomiting and yellow or green-tinted vision are typical of digoxin toxicity. Metoprolol slows AV conduction through β-receptors, not calcium channels; dofetilide blocks the rapid potassium current (IKr), and flecainide is a class Ic sodium-channel blocker.

D. Methylxanthines competitively antagonize adenosine — Adenosine slows conduction through the AV node and can interrupt re-entry there, restoring sinus rhythm in PSVT. It is antagonized competitively by methylxanthines such as caffeine and theophylline. Its half-life is under 10 seconds, which is why it is given as a rapid bolus.

E. Potassium-channel block that prolongs repolarization, maximal at slow heart rates — Sotalol has class II and class III actions. Its potassium-channel block prolongs repolarization and the QT interval, and it shows reverse use dependence — the blocking effect is greatest when the heart rate is slow, raising the risk of QT prolongation and torsades de pointes in bradycardia. Inhibiting the delayed rectifier potassium current prolongs repolarization, and an ectopic beat in that window (R-on-T) can trigger torsades. IV magnesium is the first-line drug.

B. It increased death and cardiac arrest after myocardial infarction in CAST — This describes class Ic (flecainide, propafenone): marked sodium-channel block with a wider QRS and little QT effect. In CAST, encainide or flecainide after myocardial infarction increased death or cardiac arrest (7.7% vs 3.0% on placebo), and class Ic drugs are contraindicated after myocardial infarction. The lupus-like syndrome belongs to procainamide (Ia) and pulmonary toxicity to amiodarone (III). Class Ic conserves action-potential duration; it is class Ib that reduces it. Digoxin is not a contraindication either: propafenone’s label does not list it among the contraindications, though propafenone may increase digoxin levels.

B. Fenofibrate — fibrates are mainly glucuronidated, and fenofibrate changes statin exposure only modestly — Gemfibrozil inhibits OATP1B1, a hepatic transporter, raising exposure of substrates such as atorvastatin and simvastatin; simvastatin with gemfibrozil is contraindicated, and the combination has caused rhabdomyolysis. Fibric acids are metabolized mainly by glucuronidation with minimal effect on cytochrome P450, and fenofibrate changed atorvastatin and pravastatin exposure only modestly — yet its label still advises against combining it with a statin unless the benefit outweighs the risk. Icosapent ethyl is an ethyl ester of eicosapentaenoic acid, not a fibrate.

C. The NPC1L1 sterol transporter at the intestinal brush border — Ezetimibe blocks the sterol transporter NPC1L1 at the brush border of the small intestine; it neither increases bile-acid excretion nor inhibits hepatic cholesterol synthesis. Less cholesterol reaches the liver, hepatic stores fall and LDL receptors increase, so it adds to a statin. PPAR-α is the fibrates’ target, and its activation mainly lowers triglycerides by increasing fatty-acid oxidation and VLDL catabolism.

A. Colesevelam — Colesevelam, like other bile-acid sequestrants, can increase serum triglycerides, and hypertriglyceridemia can cause acute pancreatitis. Triglycerides above 500 mg/dL are a contraindication, and colesevelam is discontinued if triglycerides exceed 500 mg/dL. Colesevelam is also indicated for glycemic control in type 2 diabetes; the others act differently: fenofibrate and icosapent ethyl lower triglycerides, ezetimibe blocks intestinal cholesterol absorption, and evolocumab blocks PCSK9 binding to the LDL receptor.

E. Lomitapide — Lomitapide inhibits microsomal triglyceride transfer protein, preventing assembly of apo B-containing lipoproteins; less VLDL synthesis lowers plasma LDL-C, and it is labelled for homozygous familial hypercholesterolemia. PCSK9 antibodies work by preserving LDL receptors, and patients with two receptor-negative alleles did not respond to evolocumab; statins lower LDL by upregulating LDL receptors, and lovastatin was less effective in homozygous familial hypercholesterolemia without functional receptors. Ezetimibe and bile-acid sequestrants such as cholestyramine also lower LDL-C by increasing hepatic LDL receptors.

A. Doxazosin — Alpha-1 receptors in the prostate and bladder neck set the smooth-muscle tone of the dynamic component of BPH, and blocking them lowers urethral resistance; doxazosin and terazosin are labeled for both BPH and hypertension. Selective alpha-1 blockers are second-line for hypertension because of orthostatic hypotension, and they are taken at night — doxazosin is started at bedtime to minimize first-dose syncope.

E. Verapamil — Nondihydropyridines such as verapamil and diltiazem depress ventricular contractility, which can precipitate or worsen heart failure in patients with reduced systolic function; they are relatively contraindicated in HFrEF. Dihydropyridines are potent vasodilators with limited effects on cardiac pacemaker activity and contractility. The other options are used in heart failure: ACE inhibitors such as lisinopril lower vascular resistance and raise cardiac output, loop diuretics such as furosemide are the cornerstone of diuretic therapy, and spironolactone reduces hospitalizations and mortality in heart failure.

D. Methyldopa — ACE inhibitors, ARBs and aliskiren all carry boxed warnings for fetal toxicity: drugs acting on the renin–angiotensin system in the second and third trimesters reduce fetal renal function and cause oligohydramnios, lung and skull hypoplasia and death, so they are stopped as soon as pregnancy is detected. Labetalol, methyldopa and long-acting nifedipine are preferred alternatives in pregnancy.

C. Thiazides are secreted by organic anion transporters in exchange for urate, increasing urate reabsorption — Loop and thiazide diuretics are anions secreted in exchange for urate through organic anion transporters, so urate is reabsorbed and gout attacks become more likely; they are contraindicated in diagnosed gout. His hypokalemia has a separate cause: more sodium reaches the aldosterone-sensitive collecting duct, which excretes potassium in exchange. Thiazides bind the chloride site of NCC, their lone target in the distal convoluted tubule — ENaC, on collecting-duct principal cells, is blocked by the potassium-sparing ENaC blockers — and hydrochlorothiazide decreases uric acid excretion rather than raising its production.

B. Argatroban — In heparin-induced thrombocytopenia all heparin, including flushes, is stopped and an alternative anticoagulant such as argatroban, bivalirudin or fondaparinux is used; argatroban and bivalirudin are short-acting, and bivalirudin is usually reserved for cardiac catheterization or cardiac surgery. Warfarin is risky in the acute phase and is held, and fondaparinux does not react with heparin-induced antibodies.

E. Andexanet alfa — Andexanet alfa is labeled for patients treated with rivaroxaban or apixaban who need reversal for life-threatening or uncontrolled bleeding. Idarucizumab reverses dabigatran, protamine reverses heparin, and vitamin K (with prothrombin complex concentrate for serious bleeding) reverses warfarin. Aminocaproic acid is an antifibrinolytic for bleeding from elevated fibrinolytic activity, not a specific reversal agent.

A. Unfractionated heparin — aPTT — Intravenous heparin is adjusted to the aPTT, checked at baseline and every 6 hours until therapeutic; the PTT tracks the intrinsic pathway and the PT the extrinsic. Warfarin is an oral drug monitored with regular INR checks, and the direct oral anticoagulants were designed to need no routine laboratory monitoring. The PT and aPTT are relatively insensitive measures of fondaparinux activity.

C. Prasugrel — Prasugrel is contraindicated in patients with a prior transient ischemic attack or stroke, and it is generally not recommended at 75 years or older. Active pathological bleeding contraindicates clopidogrel, and a history of intracranial hemorrhage contraindicates ticagrelor — neither applies here. Cangrelor’s only contraindications are significant active bleeding and hypersensitivity to the product, so a prior TIA is not one of them.

B. Low potassium leaves digoxin’s binding site on the Na⁺/K⁺-ATPase uncontested — Digoxin competes with K⁺ for its binding site on the Na⁺/K⁺-ATPase, so in diuretic-induced hypokalemia its action is unopposed. Hypokalemia potentiates digoxin toxicity, and loop diuretics carry the greatest risk of it among diuretics. Loops cause hypokalemia because more sodium reaches the distal nephron and aldosterone rises, trapping K⁺ in the lumen. In chronic toxicity the hypokalemia is corrected with potassium. Only a small fraction of digoxin is metabolized, and that metabolism does not depend on the cytochrome P-450 system; and only about 25% of plasma digoxin is protein-bound, so displacement from albumin is not the mechanism.

D. Aliskiren — Aliskiren is a direct renin inhibitor: it lowers plasma renin activity and blocks the conversion of angiotensinogen to angiotensin I. Every RAAS inhibitor removes the negative feedback on renin, so renin concentration rises with all of them. With an ACE inhibitor or an ARB the extra renin raises plasma renin activity; with aliskiren its effect is blocked, so plasma renin activity, angiotensin I and angiotensin II all fall. A thiazide such as hydrochlorothiazide raises renin secretion only through volume depletion and does not block renin, whereas β-blockers such as propranolol lower blood pressure partly by decreasing renin.

E. Epinephrine’s α1 vasoconstriction is unopposed because its β2 vasodilation is blocked — Epinephrine acts comparably on α1 and β receptors; its β2-mediated vasodilation lowers vascular resistance at low doses, and α1 vasoconstriction takes over at higher doses. In a patient on long-term propranolol, a nonselective β-blocker, epinephrine may cause uncontrolled hypertension because its α-receptor stimulation is unopposed. A β1-selective blocker such as metoprolol does not reverse epinephrine’s β2-mediated vasodilation. β-Blockers lower blood pressure partly by decreasing renin, not raising it.

A. Switch to a loop diuretic such as furosemide — When diuresis is the main goal in chronic kidney disease, thiazides are contraindicated and loop diuretics are preferred; the one exception is metolazone, a thiazide diuretic that can be used for diuresis in CKD. Loop diuretics are the favored initial therapy for fluid overload in renal insufficiency.

C. Amiodarone — Amiodarone is a major warfarin interaction: it potentiates warfarin’s effect by two different mechanisms. The amiodarone label also warns that it potentiates the anticoagulant response, so the INR is monitored closely when the two are combined. Warfarin interacts with many medications, so the label is checked before another drug is added. The other four were studied with warfarin: nebivolol had no significant effect on its anticoagulant activity (prothrombin time and INR), losartan showed no clinically significant interaction, amlodipine did not affect the warfarin prothrombin response time, and bumetanide had no effect on warfarin metabolism or prothrombin activity.

E. Sotalol — Sotalol has both class II (β-blocking) and class III properties, and its label lists bronchial asthma and related bronchospastic conditions as contraindications. Non-selective β-blockers should not be used in patients with asthma. Dofetilide, by contrast, blocks only the rapid delayed-rectifier potassium current (IKr) and has no effect on α- or β-receptors. Procainamide (class Ia) and flecainide (class Ic) are class I sodium-channel blockers, and mexiletine is a class Ib agent; β-blockade is the class II action, which sotalol shares with its class III properties.

D. Increased lithium reabsorption in the proximal tubule — Thiazides can cause lithium accumulation by increasing its reabsorption in the proximal tubule. Diuretics reduce lithium’s renal clearance and add a high risk of lithium toxicity, and ACE inhibitors also reduce its renal clearance — so her lithium already needed monitoring on lisinopril, and the thiazide added to the risk. Lithium is neither protein-bound nor metabolized and is almost completely absorbed after oral use; it is eliminated almost entirely by the kidneys, so a change in its renal handling is what raises its level.

C. Volume depletion from recent intensive diuresis — First-dose hypotension with ACE inhibitors is more common in patients who are volume-depleted or receiving high-dose diuretics, and in those with high baseline renin. In patients recently started on diuretics, the first dose of captopril may cause a precipitous fall in blood pressure, usually within the first hour, because it blocks the angiotensin II formed from compensatory renin release. Excessive loop diuresis lowers renal blood flow and GFR, causing prerenal azotemia and orthostatic hypotension.

E. Cholestyramine — Cholestyramine is an anion-exchange resin that binds acidic drugs such as warfarin in the gut, delaying or reducing their absorption, so other drugs are taken well apart from it. Fibrates do the opposite: they potentiate coumarin anticoagulants and prolong the PT/INR, and gemfibrozil is highly protein-bound, with potential for displacement interactions. Atorvastatin and icosapent ethyl, by contrast, did not change warfarin’s anticoagulant effect in their label interaction studies.

A. Additive slowing of AV-node conduction by L-type calcium-channel block and β-blockade — Verapamil blocks L-type calcium channels, with high affinity for both myocardial tissue and vascular smooth muscle; it slows AV conduction by reducing calcium-dependent depolarization in nodal tissue, and nondihydropyridine CCBs cause bradycardia and AV conduction delay that is particularly hazardous with β-blockers or digoxin. Combined with a β-blocker, verapamil has additive negative effects on heart rate, AV conduction and contractility, and complete heart block has been reported. β-Blocker labels likewise warn that verapamil and diltiazem add to their slowing of AV conduction and heart rate. Metoprolol would not accumulate in renal failure: it is eliminated mainly by metabolism in the liver, with very little excreted unchanged in the urine.

B. Hydrochlorothiazide — The dofetilide label contraindicates hydrochlorothiazide (alone or with triamterene) and verapamil, as well as the renal cation-transport inhibitors cimetidine, trimethoprim and ketoconazole. Dofetilide can cause torsades de pointes, and its QT prolongation is directly related to plasma concentration, which low creatinine clearance and drug interactions raise. To minimize the risk of induced arrhythmia, it is started in a facility with continuous ECG monitoring.

D. Diltiazem inhibits CYP3A4, raising ivabradine exposure, and slows the heart itself — Ivabradine is metabolized mainly by CYP3A4, and moderate CYP3A4 inhibitors such as diltiazem and verapamil should be avoided with it; higher ivabradine levels may exacerbate bradycardia and conduction disturbances. Diltiazem itself causes bradycardia and AV conduction delay, especially with a β-blocker, and its negative inotropy makes nondihydropyridines hazardous in systolic heart failure.

C. Spironolactone — Potassium-sparing diuretics — ENaC blockers directly, aldosterone antagonists such as spironolactone indirectly — suppress K⁺ and H⁺ secretion in the distal nephron, causing hyperkalemia and a hyperchloremic (normal-anion-gap) metabolic acidosis. The hyperkalemia also impairs ammonia excretion, and bicarbonate is used up buffering it. An ACE inhibitor adds to the potassium rise, because without angiotensin II aldosterone falls. Loop and thiazide diuretics do the opposite — hypokalemia and metabolic alkalosis, more often with loops.

A. Isosorbide dinitrate (arteries and veins, via nitric oxide) and hydralazine (arterioles) — The combination pairs isosorbide dinitrate, a nitrate that dilates both arteries and veins by releasing nitric oxide and activating guanylyl cyclase, with hydralazine, an arteriolar vasodilator. It is indicated as an adjunct to standard therapy in self-identified Black patients with heart failure to improve survival and prolong time to heart-failure hospitalization.

B. Milrinone — Milrinone selectively inhibits phosphodiesterase III in cardiac and vascular muscle; the resulting rise in cAMP increases intracellular calcium and contractility, and it is not a β-agonist. Phosphodiesterase inhibitors such as milrinone raise cAMP and can increase inotropy even in β-blocker poisoning. Dobutamine (β1 > β2 > α) and isoproterenol (nonselective β) act through β-receptors, dopamine raises contractility through β1 at intermediate rates, and epinephrine acts on α1 and β receptors.