Loop Diuretics

IV loop diuretics treat hypervolemia in acute DCM exacerbation. In RCM they are the mainstay but must be watched closely — excessive diuresis removes the high filling pressure the stiff ventricle needs. In HCM only carefully, in patients without outflow obstruction and with volume overload. In PPCM during pregnancy, low doses only, because they may reduce placental perfusion.

First-line for volume-overload states (heart failure, cirrhosis, renal disease, edema): blocking the Na-K-2Cl cotransporter in the thick ascending limb produces potent diuresis — at the cost of potassium, calcium, and magnesium losses. On therapy, monitor electrolytes, renal function, BP, and the daily weight. In hypercalcemia they are no longer routine — volume repletion with 0.9% saline comes first, if loops are used at all.

The congestion reliever: clears the volume overload behind the dyspnea and edema. Improves symptoms, not mortality — and wastes potassium, so pair every dose with the K⁺ trend.

[Ototoxicity] Loop diuretics are ototoxic but their effects are described as "acute but completely reversible" (StatPearls). Report hearing changes.

Only after rehydration. "Loop diuretics should not be used until the patient is adequately rehydrated"; with zoledronic acid they "may increase risk of hypocalcemia."

For hypercalcemia — but only after the patient is rehydrated. "Loop diuretics, which promote urinary calcium excretion by inhibiting calcium reabsorption at the loop of Henle, should only be administered after adequate IV resuscitation is achieved." Hydration comes first because dehydration worsens hypercalcemia — patients are advised "to stay well hydrated to prevent worsening of calcium levels." Loop diuretics also appear on the list of drugs that can lower calcium.

Treats the heart-failure cause of the commonest transudate. When heart failure is confidently suspected a trial of diuresis comes before a tap, and thoracentesis in heart failure is recommended only if diuretics fail or the patient is significantly symptomatic.

Diuretic therapy for PAH patients with fluid retention and right-ventricular failure, with a low-salt diet to help control body fluids.

TACO — "Management involves diuretics and ventilatory support"; diuretics before or between transfusions help prevent it in at-risk patients. May also be needed to maintain urine output in acute hemolysis. Use with caution in TRALI, where diuretics "may result in hypotension."

First-line for hypertension — a milder diuretic acting further down the nephron. Remember the four metabolic highs — glucose, lipids, uric acid and calcium — and that the calcium rise comes from retention (opposite of loops).

Weak diuretics that preserve potassium instead of wasting it — the defining danger is hyperkalemia. Two mechanisms; spironolactone also lowers heart-failure mortality.

Two diuretic groups that are used mostly for something other than edema: the carbonic anhydrase inhibitors acetazolamide and methazolamide (glaucoma, altitude sickness) and the osmotic diuretic mannitol (raised intracranial or intraocular pressure). Watch for metabolic acidosis, low potassium and serious sulfonamide reactions with the first group, and for fluid overload, kidney injury and electrolyte swings with mannitol.

Tolvaptan blocks vasopressin’s V2 receptor in the kidney so the body sheds free water and serum sodium rises (Samsca, for hyponatremia), and it slows kidney decline in polycystic kidney disease (Jynarque). The two brands carry different boxed warnings: correcting sodium too fast, and serious liver injury.

Replacing potassium, magnesium, calcium, phosphate & fluids, and correcting acidosis with IV bicarbonate. IV potassium is high-alert — NEVER push it.

Gut-acting drugs that bind potassium in the intestine so it leaves in the stool. Their onset is delayed, so they are not emergency treatment for life-threatening hyperkalemia. Watch for low potassium, the sodium they carry (sodium polystyrene sulfonate, Lokelma), low magnesium (Veltassa) and their effects on other oral drugs.