Lab values & drug levels

A high-yield NCLEX table. It keeps two things separate: a therapeutic drug level is the target you dose the drug to reach (digoxin, lithium); a normal range is the healthy baseline you monitor to stay within (LFTs, potassium). Values are typical adult figures for orientation — always read against your facility's reference range and the patient's clinical picture.

147 monitored levels

Test · drug class Therapeutic / normal Toxic / critical

24-hour urine free cortisol and serum or plasma cortisol (osilodrostat) Every 1 to 2 weeks during titration, then at least every 1 to 2 months once the maintenance dose is reached Adrenal Agents

—

Toxic / critical —

25-hydroxy vitamin D Before starting an aromatase inhibitor (exemestane label); supplement if deficient Aromatase inhibitors

—

Toxic / critical —

Absolute neutrophil count (ANC) Monitor with the CBC to track neutrophil recovery Colony-Stimulating Factors

Normal range ≥ 1,500/µL (adults typically ~2,500–7,000; neutropenia below 1,500, severe below 500)

Toxic / critical —

ALT, AST and bilirubin (Jynarque) Before starting, at 2 and 4 weeks, monthly for the first 18 months, then every 3 months Vasopressin Antagonists

—

Toxic / critical —

Amniotic fluid by ultrasound (indomethacin) Consider if NSAID treatment extends beyond 48 hours Tocolytics

—

Toxic / critical —

aPTT (argatroban, for HIT) During the infusion; argatroban also raises the INR when overlapped with warfarin Anticoagulants

Therapeutic 1.5–3× the initial baseline value (not above 100 seconds)

Toxic / critical —

aPTT (heparin) q6h until stable on IV heparin Anticoagulants

Therapeutic 1.5–2× normal (or anti-Xa)

Toxic / critical —

AST / ALT (LFTs) If overdose or chronic/high-dose use Acetaminophen (Non-Opioid Analgesic)

Normal range Typical ALT 4–36 · AST 5–30 IU/L (lab-specific)

Toxic / critical —

Blood glucose Before meals & bedtime; match insulin to glucose/meal Insulins

Therapeutic 80–130 mg/dL before meals; below 180 mg/dL 1–2 h after meals (most non-pregnant adults; individualized)

Toxic / critical < 70 mg/dL = hypoglycemia — treat immediately

Blood glucose Frequently when starting pramlintide or a glinide, and when other glucose-lowering drugs are adjusted Other Antidiabetics

—

Toxic / critical —

Blood glucose After the rescue dose until the patient is awake and has eaten; during diagnostic use in patients with diabetes or on insulin, and in patients taking indomethacin Glucagon Agents

—

Toxic / critical —

Blood glucose At regular intervals during prolonged therapy (labels include a 2-hour after-meal glucose); esp. diabetics Corticosteroids

Normal range Fasting 70–99 mg/dL

Toxic / critical Steroids raise glucose (hyperglycemia) — more after meals than when fasting

Blood glucose When a somatostatin analog is started or its dose changed; periodically with somatropin; in diabetic patients on pegvisomant Pituitary Hormone Agents

—

Toxic / critical —

Blood glucose Bicalutamide with an LHRH agonist; abiraterone in patients with diabetes Antiandrogens & 5α-Reductase Inhibitors

—

Toxic / critical —

Blood glucose (niacin) Closely in diabetic or prediabetic patients, especially in the first months and after dose changes Other Lipid-Lowering Agents

—

Toxic / critical —

Blood glucose and lipids Periodically during androgen deprivation therapy for prostate cancer GnRH Agonists & Antagonists

—

Toxic / critical —

Blood glucose and potassium (terbutaline) During therapy; monitor the newborn for hypoglycemia Tocolytics

—

Toxic / critical —

Blood pressure Periodically during therapy, especially in men with hypertension Androgens

—

Toxic / critical —

Blood pressure When starting with an α-blocker or antihypertensives, and after adding CYP3A4 inhibitors PDE5 inhibitors

—

Toxic / critical —

Blood pressure Monitor regularly — ESAs can raise/worsen hypertension Erythropoiesis-Stimulating Agents (ESAs)

Normal range < 120/80 mmHg (normal)

Toxic / critical —

Blood pressure (methylergonovine) During treatment, and carefully throughout if given IV Uterotonics

—

Toxic / critical —

Blood pressure and heart rate Epoprostenol: standing and supine, closely for several hours after each dose adjustment. Riociguat: at initiation and before each dose increase (up-titrated only if systolic pressure stays above 95 mmHg without hypotension). Pulmonary Hypertension Agents

—

Toxic / critical —

Blood pressure and serum electrolytes (fludrocortisone) Regularly; periodic serum electrolytes during prolonged therapy Adrenal Agents

—

Toxic / critical —

Blood pressure, potassium and fluid retention Abiraterone: at least monthly Antiandrogens & 5α-Reductase Inhibitors

—

Toxic / critical —

Body weight (minoxidil) Daily (the patient weighs at home) Other Antihypertensives

—

Toxic / critical Quick gain of 5 lb or more, or new swelling → fluid retention; notify

Bone mineral density Women with risk factors for bone loss on elagolix; before retreatment with leuprolide for endometriosis GnRH Agonists & Antagonists

—

Toxic / critical —

Bone mineral density (DXA) At baseline before treatment, then periodically during therapy Aromatase inhibitors

—

Toxic / critical —

Breast examination and mammography Yearly clinical breast examination; mammography scheduled by age, risk factors and prior results Menopausal Hormone Therapy, Progestins & Antiprogestins

—

Toxic / critical —

Calcium Monitor Thiazide Diuretics

Normal range Typically 8.5–10.5 mg/dL (varies by lab)

Toxic / critical Hypercalcemia (thiazides retain calcium)

Calcium Tamoxifen and toremifene in breast cancer with bone metastases, especially in the first weeks Selective Estrogen Receptor Modulators (SERMs)

—

Toxic / critical —

Carbamazepine level Trough; also baseline and periodic CBC and liver function; watch for hyponatremia Anticonvulsants

Therapeutic 4–12 mcg/mL

Toxic / critical > 12 mcg/mL — ataxia, nystagmus, disorientation; seizures and coma > 25

CBC Periodically during the first 12 months Fibrates

—

Toxic / critical —

CBC & LFTs (± renal function) Baseline & periodically on methotrexate — detects myelosuppression/hepatotoxicity Immunosuppressants / Biologics / DMARDs

Normal range WBC about 4,500–11,000/µL · Hgb 13–18 g/dL (men), 12–16 (women) · Plt 150,000–400,000/µL; typical ALT 4–36 · AST 5–30 IU/L (lab-specific)

Toxic / critical —

CBC and direct Coombs test (methyldopa) Blood count before starting and periodically; Coombs test before therapy and at 6 and 12 months Other Antihypertensives

—

Toxic / critical Coombs-positive hemolytic anemia → stop methyldopa; do not restart

CBC and platelet count (acetazolamide, methazolamide) Baseline before starting and at regular intervals during therapy Carbonic Anhydrase Inhibitors & Osmotic Diuretics

—

Toxic / critical —

Chest X-ray Nilutamide: before starting Antiandrogens & 5α-Reductase Inhibitors

—

Toxic / critical —

Clozapine — absolute neutrophil count (ANC) Weekly for the first 6 months, then less frequently (agranulocytosis surveillance) Antipsychotics

Normal range Baseline ≥ 1500/µL (≥ 1000 for benign ethnic neutropenia)

Toxic / critical < 500/µL = severe neutropenia — stop clozapine

Complete blood count with platelets; liver function tests Periodically during tamoxifen or toremifene therapy Selective Estrogen Receptor Modulators (SERMs)

—

Toxic / critical —

Creatine kinase (CK) Check if the patient reports muscle pain, tenderness, or weakness Statins

Normal range Lab-specific (upper limit of normal about 100–400 U/L)

Toxic / critical > 10× ULN with muscle symptoms = myopathy; markedly elevated CK or suspected myopathy → stop the statin

Creatine kinase (CK) If muscle pain, tenderness or weakness develops Fibrates

—

Toxic / critical Markedly elevated, or myopathy suspected → stop the fibrate

Digoxin level Draw ≥ 6–8 h after the last dose Cardiac Glycosides (Digoxin)

Therapeutic 0.8–2 ng/mL (label: < 0.5 less effective, > 2 more toxic); heart failure: 0.5–0.9 ng/mL

Toxic / critical > 2 ng/mL raises toxicity risk (> 2.4 toxic per StatPearls)

ECG (osilodrostat) Before starting, within one week after starting, and as clinically indicated Adrenal Agents

—

Toxic / critical —

ECG and electrolytes In men with QT risk factors on androgen deprivation therapy GnRH Agonists & Antagonists

—

Toxic / critical —

ECG, potassium and magnesium Toremifene: electrolytes corrected before starting and monitored periodically; ECG at baseline and as indicated in patients at increased risk Selective Estrogen Receptor Modulators (SERMs)

—

Toxic / critical —

Echocardiogram (cabergoline, bromocriptine) Before starting, then every 6 to 12 months or as clinically indicated Pituitary Hormone Agents

—

Toxic / critical —

Electrolytes (K⁺, Na⁺) Baseline & routinely — loop/thiazide lower K⁺, potassium-sparing agents raise it Diuretics

Normal range K⁺ 3.5–5.0 · Na⁺ 135–145 mEq/L

Toxic / critical —

GH and IGF-1 To judge acromegaly treatment with the somatostatin analogs; IGF-1 alone with pegvisomant (GH assays read falsely high) Pituitary Hormone Agents

—

Toxic / critical —

Glucose Monitor, esp. in diabetics Thiazide Diuretics

Normal range Fasting 70–99 mg/dL

Toxic / critical Hyperglycemia (one of the metabolic highs)

Hematocrit and hemoglobin Before starting and periodically during therapy Androgens

—

Toxic / critical —

Hemoglobin (Hgb) CKD: at least weekly when starting or adjusting the dose until stable, then at least monthly; reduce the dose if Hgb rises more than 1 g/dL in any 2-week period Erythropoiesis-Stimulating Agents (ESAs)

Therapeutic No safe target; CKD on dialysis: reduce/interrupt as Hgb approaches 11 g/dL (CKD not on dialysis: above 10 g/dL); chemotherapy: start only if Hgb is below 10 g/dL with at least 2 more months of chemotherapy planned, and withhold above the level needed to avoid transfusion

Toxic / critical —

Hemoglobin / hematocrit After mifepristone if bleeding is heavy Menopausal Hormone Therapy, Progestins & Antiprogestins

—

Toxic / critical —

Hemoglobin / hematocrit (ERAs) Bosentan: after 1 and 3 months, then every 3 months. Ambrisentan: before starting, at 1 month, then periodically. Macitentan: before starting, then as clinically indicated. Pulmonary Hypertension Agents

—

Toxic / critical —

INR (lomitapide with warfarin) Regularly, especially when the lomitapide dose changes Other Lipid-Lowering Agents

—

Toxic / critical —

INR (patients on warfarin) With colesevelam, frequently during initiation and then periodically. Bile Acid Sequestrants

—

Toxic / critical —

INR (warfarin) Routine; more often when starting/adjusting Anticoagulants

Therapeutic 2.0–3.0 (2.5–3.5 mechanical mitral valve)

Toxic / critical > 4 → bleeding risk

Intact PTH During cinacalcet — adynamic bone disease may develop if iPTH is suppressed below 100 pg/mL Bone and Calcium Agents

—

Toxic / critical —

LDL cholesterol (LDL-C) Assess when clinically appropriate; the effect can be measured as early as 4 weeks after starting. With once-monthly evolocumab or every-4-week alirocumab, measure just before the next dose, because LDL-C can vary across the dosing interval. PCSK9 Inhibitors

—

Toxic / critical —

LFTs (AST/ALT) Baseline & during azole therapy — azoles can be hepatotoxic; also check regularly during caspofungin (echinocandin) therapy, which can raise AST/ALT Systemic Antifungals

Normal range Typical ALT 4–36 · AST 5–30 IU/L (lab-specific)

Toxic / critical —

LFTs (hepatic function) Baseline & periodically — hepatotoxicity (boxed warning): reduce the dose or stop if transaminases exceed 3× normal (or double from an elevated baseline); stop for signs of clinical liver injury Antiarrhythmics

Normal range Typical ALT 4–36 · AST 5–30 IU/L (lab-specific)

Toxic / critical —

Lipid panel (LDL-C, triglycerides) Baseline including triglycerides; colesevelam within 4–6 weeks of starting; cholestyramine frequently in the first months, then periodically. Bile Acid Sequestrants

—

Toxic / critical Colesevelam: triglycerides > 500 mg/dL → stop; > 300 mg/dL → closer monitoring

Lipid profile Periodically, particularly after starting therapy Androgens

—

Toxic / critical —

Lipids LDL-C as early as 4 weeks after ezetimibe and 30 days after inclisiran; triglycerides and HDL-C 4 weeks after starting bempedoic acid with a fibrate Other Lipid-Lowering Agents

—

Toxic / critical —

Lipids (triglycerides and HDL-C) Triglycerides 4–8 weeks after starting fenofibrate; HDL-C within the first few months (paradoxical fall); stop if no adequate response after 2 months (fenofibrate) or 3 months (gemfibrozil) Fibrates

—

Toxic / critical —

Lithium level Draw 12 h after the dose; check frequently when starting Mood Stabilizers (Lithium)

Therapeutic 0.6–1.2 mEq/L (maintenance)

Toxic / critical > 1.5 mEq/L

Liver aminotransferases (ALT, AST) and bilirubin (ERAs) Bosentan: before starting, then monthly (REMS). Macitentan: baseline, then as clinically indicated. Pulmonary Hypertension Agents

—

Toxic / critical Bosentan: generally avoided if > 3× ULN at baseline; stop if elevated with liver-injury symptoms or bilirubin ≥ 2× ULN

Liver function (ALT, AST, bilirubin) Baseline and periodically (fenofibrate); periodically (gemfibrozil) Fibrates

—

Toxic / critical ALT or AST persistently > 3 × ULN, or with a rising bilirubin → stop fenofibrate

Liver function (lomitapide) ALT, AST, alkaline phosphatase and bilirubin before starting; ALT/AST before each dose increase or monthly in the first year, then at least every 3 months Other Lipid-Lowering Agents

—

Toxic / critical ALT or AST ≥ 3 × ULN → reduce or withhold; symptoms or bilirubin ≥ 2 × ULN → stop

Liver function (niacin) Before starting, every 6–12 weeks for the first year, then periodically (about every 6 months) Other Lipid-Lowering Agents

—

Toxic / critical Progressive rise, especially persistent ≥ 3 × ULN or with symptoms → stop

Liver function tests (AST/ALT, bilirubin) Baseline & periodically — isoniazid, rifampin, and pyrazinamide are hepatotoxic; hold and notify for symptomatic hepatitis (nausea, dark urine, jaundice, RUQ pain). Antitubercular Agents

Normal range Typical ALT 4–36 · AST 5–30 IU/L · total bilirubin < 1 mg/dL (2–17 µmol/L) (lab-specific)

Toxic / critical —

Liver function tests (methyldopa) Before starting, then periodically — especially the first 6–12 weeks or with unexplained fever Other Antihypertensives

—

Toxic / critical Fever, abnormal liver tests or jaundice → stop methyldopa; do not restart

Liver function tests (methyltestosterone, danazol) Periodically during therapy Androgens

—

Toxic / critical —

Liver function tests (transaminases) Before starting, then only when clinically indicated (e.g., symptoms of liver injury) Statins

Normal range Typical ALT 4–36 · AST 5–30 IU/L (lab-specific)

Toxic / critical Serious liver injury (symptoms, hyperbilirubinemia, or jaundice) → stop promptly; > 3× ULN → closer monitoring, dose reduction, or discontinuation

Liver function tests and blood count At baseline before treatment Aromatase inhibitors

—

Toxic / critical —

Liver tests With elagolix, and with degarelix, which commonly raises transaminases GnRH Agonists & Antagonists

—

Toxic / critical —

Liver tests (ALT, AST, alkaline phosphatase, bilirubin) Pioglitazone: before starting and promptly for symptoms of liver injury. Acarbose: transaminases every 3 months in the first year, then periodically Other Antidiabetics

—

Toxic / critical —

Liver tests (AST, ALT, bilirubin) Fezolinetant: before starting, then monthly for the first 3 months and at 6 and 9 months, and promptly for symptoms of liver injury Menopausal Hormone Therapy, Progestins & Antiprogestins

—

Toxic / critical —

Liver tests (pegvisomant) Before starting, then monthly for 6 months, quarterly for the next 6 months and twice yearly for the next year Pituitary Hormone Agents

—

Toxic / critical —

Liver tests (transaminases; bilirubin with abiraterone) Flutamide, bicalutamide, nilutamide: before starting, regularly for the first 4 months, then periodically; abiraterone: before starting, every two weeks for 3 months, then monthly Antiandrogens & 5α-Reductase Inhibitors

—

Toxic / critical —

Maternal heart rate, blood pressure and fetal heart rate Throughout tocolysis Tocolytics

—

Toxic / critical —

Max daily dose Count all combination OTC products Acetaminophen (Non-Opioid Analgesic)

Therapeutic ≤ 4 g/day adult (some OTC labels cap at 3 g); ≤ 2 g with chronic alcohol use; reduced in liver impairment

Toxic / critical Hepatotoxic above ceiling / acute overdose

Methotrexate dosing frequency Verify the schedule at every check — accidental daily dosing is a classic, sometimes fatal, error Immunosuppressants / Biologics / DMARDs

Therapeutic WEEKLY for autoimmune disease

Toxic / critical DAILY dosing can be fatal (pancytopenia/mucositis)

Morning serum testosterone On at least two separate days to confirm hypogonadism before starting; then periodically to keep levels in range Androgens

—

Toxic / critical —

NT-proBNP rather than BNP (sacubitril/valsartan) When worsening heart failure is suspected — BNP is a neprilysin substrate and rises on the drug; NT-proBNP is not Heart Failure Agents

—

Toxic / critical —

Peak Draw 30 min after the IV infusion ends Aminoglycosides

Therapeutic 5–10 mcg/mL (gentamicin, conventional dosing)

Toxic / critical > 12 mcg/mL (gentamicin, tobramycin; amikacin > 35)

Phenytoin level Trough, just before the next dose; draw a free (unbound) level in low-albumin or renal-failure patients Anticonvulsants

Therapeutic 10–20 mcg/mL (narrow therapeutic index)

Toxic / critical > 20 mcg/mL — nystagmus, ataxia, then CNS depression

Phosphorus, potassium, calcium and magnesium (potassium phosphates) Before and during treatment; check potassium and calcium first and normalize calcium before giving it Electrolyte & Fluid Replacement

—

Toxic / critical —

Plasma bicarbonate and blood gases (sodium bicarbonate) Periodically during stepwise correction, to avoid overdosage and alkalosis Electrolyte & Fluid Replacement

Normal range 24–31 mEq/L (plasma bicarbonate)

Toxic / critical —

Platelets Baseline & periodically Anticoagulants

Normal range About 150,000/µL or more (lab-specific); on heparin, < 100,000/mm³ → stop and evaluate for HIT

Toxic / critical Watch for HIT (heparin)

Platelets, PT and phosphorus (niacin) Platelets and PT closely with anticoagulants; phosphorus periodically if at risk of hypophosphatemia Other Lipid-Lowering Agents

—

Toxic / critical —

Potassium Baseline & routine Loop Diuretics

Normal range 3.5–5.0 mEq/L

Toxic / critical Hypokalemia common

Potassium Baseline & routine Thiazide Diuretics

Normal range 3.5–5.0 mEq/L

Toxic / critical Hypokalemia common

Potassium Baseline & routine Potassium-Sparing Diuretics

Normal range 3.5–5.0 mEq/L

Toxic / critical Hyperkalemia > 5.0 mEq/L

Potassium Confirm urine output before replacing Electrolyte & Fluid Replacement

Normal range 3.5–5.0 mEq/L

Toxic / critical < 3.5 or > 5.0 mEq/L

Potassium Monitor Corticosteroids

Normal range 3.5–5.0 mEq/L

Toxic / critical May fall (hypokalemia)

Potassium (K⁺) Before dosing & routinely Cardiac Glycosides (Digoxin)

Normal range 3.5–5.0 mEq/L

Toxic / critical Low K⁺ potentiates toxicity

Potassium / magnesium & renal function (SCr) During amphotericin B — it wastes K⁺/Mg²⁺ and is nephrotoxic; with liposomal amphotericin, a high serum phosphate may be falsely elevated by some assays Systemic Antifungals

Normal range K⁺ 3.5–5.0 mEq/L · Mg about 1.8–2.2 mg/dL · SCr about 0.6–1.2 mg/dL in men, 0.5–1.1 in women (varies by lab)

Toxic / critical —

Pregnancy test (danazol) Immediately before starting therapy Androgens

—

Toxic / critical —

Pregnancy test (ERAs and riociguat, in females of reproductive potential) Before starting; pregnancy must be excluded before the first dose. Pulmonary Hypertension Agents

—

Toxic / critical —

Pregnancy test (females of reproductive potential) Before starting letrozole; within 7 days before starting exemestane Aromatase inhibitors

—

Toxic / critical —

Pregnancy test (lomitapide) Before starting, in females of reproductive potential Other Lipid-Lowering Agents

—

Toxic / critical Positive → do not start (contraindicated)

Pregnancy test (mifepristone) Before starting, and if treatment is interrupted for more than 14 days, in females of reproductive potential Adrenal Agents

—

Toxic / critical —

Pregnancy test (vericiguat) Before starting, in females of reproductive potential Heart Failure Agents

—

Toxic / critical Positive → do not start (contraindicated in pregnancy)

Pregnancy test and CBC (sodium iodide I-131) Pregnancy test within 24 hours before treatment in females of reproductive potential; complete blood count within one month of therapy Thyroid Agents

—

Toxic / critical —

Prothrombin time / INR Flutamide, bicalutamide or nilutamide with warfarin Antiandrogens & 5α-Reductase Inhibitors

—

Toxic / critical —

PSA 5α-reductase inhibitors: new baseline after several months, then periodically (any confirmed rise is evaluated); prostate cancer drugs: regularly to monitor response Antiandrogens & 5α-Reductase Inhibitors

—

Toxic / critical —

PSA and prostate evaluation Before starting and periodically during therapy Androgens

—

Toxic / critical —

PT/INR (with warfarin) Frequently until stable after a fibrate is added Fibrates

—

Toxic / critical —

Pulmonary — chest x-ray / PFTs Baseline chest x-ray and PFTs (including diffusion capacity), then history, exam, and chest x-ray every 3–6 months (boxed warning) — watch for pulmonary fibrosis / pneumonitis Antiarrhythmics

Normal range Clear CXR; normal DLCO at baseline

Toxic / critical —

QT interval / ECG Intermittent or continuous ECG during initial therapy and dose changes; continuous ECG when sotalol, dofetilide or IV ibutilide is started — a lengthening QT warns of torsades Antiarrhythmics

Normal range QTc ≤ 440 ms (M) / ≤ 460 ms (F)

Toxic / critical > 500 ms → torsades de pointes risk

Renal function (SCr / BUN) Baseline & during therapy Aminoglycosides

Normal range SCr about 0.6–1.2 mg/dL in men, 0.5–1.1 in women · BUN about 7–20 mg/dL (vary by lab)

Toxic / critical —

Renal function (SCr) Baseline & during therapy Vancomycin (Glycopeptide)

Normal range SCr about 0.6–1.2 mg/dL in men, 0.5–1.1 in women (varies by lab)

Toxic / critical —

Renal function (serum creatinine / eGFR) Before fenofibrate and periodically, especially in renal impairment, older or diabetic patients Fibrates

—

Toxic / critical eGFR < 30 → fenofibrate contraindicated; gemfibrozil has worsened renal insufficiency when creatinine is above 2.0 mg/dL

Serum calcium Before and during denosumab (especially in advanced kidney disease and the first weeks of Xgeva), during cinacalcet, twice weekly while calcitriol is being adjusted; correct low calcium before denosumab or romosozumab Bone and Calcium Agents

—

Toxic / critical —

Serum cholesterol / lipid profile At baseline and during therapy Aromatase inhibitors

—

Toxic / critical —

Serum creatinine / renal function (sacubitril/valsartan) Closely, especially in patients whose renal function depends on the RAAS or with renal artery stenosis Heart Failure Agents

—

Toxic / critical Clinically significant fall in renal function → down-titrate or interrupt

Serum digoxin concentration (with mirabegron or vibegron) Before starting vibegron; during therapy with either drug to titrate digoxin; continue after vibegron is stopped Overactive Bladder Agents

—

Toxic / critical —

Serum electrolytes (acetazolamide, methazolamide) Periodically during therapy Carbonic Anhydrase Inhibitors & Osmotic Diuretics

—

Toxic / critical —

Serum magnesium (and calcium with SPS) During treatment; consider magnesium supplementation if it falls on patiromer Potassium Binders

—

Toxic / critical —

Serum magnesium (obstetric) With clinical checks (DTRs, RR, urine output) Magnesium Sulfate (Obstetric)

Therapeutic 4–7 mEq/L in preeclampsia/eclampsia (StatPearls); the FDA label gives an effective anticonvulsant range of 2.5–7.5 mEq/L

Toxic / critical Patellar reflexes lost 8–10 mEq/L · respiratory depression 10–15 mEq/L · cardiac arrest 25–30 mEq/L (StatPearls); the FDA label notes reflexes fade above 4 mEq/L, and heart block may occur at or below the level where reflexes disappear

Serum osmolarity, osmol gap, electrolytes, acid–base balance and urine output (mannitol) During and after the infusion, with renal, cardiac and pulmonary function Carbonic Anhydrase Inhibitors & Osmotic Diuretics

—

Toxic / critical —

Serum phosphate (calcium × phosphate product) During calcitriol — the product should not exceed 70 mg²/dL² Bone and Calcium Agents

—

Toxic / critical —

Serum potassium After starting tolvaptan if potassium is above 5 mEq/L or the patient takes drugs that raise potassium (ACE inhibitors, ARBs, potassium-sparing diuretics) Vasopressin Antagonists

—

Toxic / critical —

Serum potassium Throughout treatment, adjusting the dose to the target range; with SPS, frequently within each 24-hour period; on hemodialysis, the pre-dialysis value Potassium Binders

Normal range 3.5–5.0 mEq/L

Toxic / critical —

Serum potassium (sacubitril/valsartan) Periodically, especially with severe renal impairment, diabetes, hypoaldosteronism or a high-potassium diet Heart Failure Agents

—

Toxic / critical —

Serum potassium and magnesium (osilodrostat, mifepristone) Corrected before starting; mifepristone potassium 1 to 2 weeks after starting or increasing the dose and periodically after Adrenal Agents

—

Toxic / critical —

Serum potassium and renal function (aliskiren) Periodically, including with an NSAID or another RAAS drug Other Antihypertensives

—

Toxic / critical Clinically significant fall in renal function → consider withholding or stopping

Serum pregnancy test (misoprostol in women of childbearing potential) Negative within 2 weeks before starting Uterotonics

—

Toxic / critical —

Serum prolactin (cabergoline) To titrate to a normal level, and periodically after stopping Pituitary Hormone Agents

—

Toxic / critical —

Serum sodium Confirm a normal sodium before starting or resuming desmopressin; recheck within 7 days and about 1 month after starting, then periodically (more often at 65 or older or with other hyponatremia risks — DDAVP Injection boxed warning); daily weights during therapy Pituitary / ADH Agents

Normal range 135–145 mEq/L

Toxic / critical Dilutional hyponatremia — headache, confusion, cerebral edema, seizures

Serum sodium (Samsca) Closely in hospital during initiation and after each dose change; keep checking that sodium stays within normal limits Vasopressin Antagonists

Normal range 135–145 mEq/L

Toxic / critical —

Serum sodium, fluid balance and neurologic status (3% saline, lactated Ringer’s) During infusion — rapid correction of hyponatremia risks serious neurologic complications Electrolyte & Fluid Replacement

—

Toxic / critical —

Sodium & renal function Monitor Loop Diuretics

Normal range Na⁺ 135–145 mEq/L · SCr about 0.6–1.2 mg/dL in men, 0.5–1.1 in women (varies by lab)

Toxic / critical —

Testosterone (or LH, FSH and sex steroids in children) To confirm suppression in prostate cancer or central precocious puberty GnRH Agonists & Antagonists

—

Toxic / critical —

Theophylline level Check whenever a status change or interacting drug alters clearance — more often in neonates, infants, older adults, and with heart failure, fever, liver disease, hypothyroidism or sepsis Methylxanthines (Theophylline)

Therapeutic 10–20 mcg/mL in adults (labels target peaks of 10–15; children 5–15) — narrow therapeutic index

Toxic / critical > 20 mcg/mL

Thyroid function In women on thyroid replacement who start estrogen (estrogen raises thyroid-binding globulin) Menopausal Hormone Therapy, Progestins & Antiprogestins

—

Toxic / critical —

Thyroid function (TSH, free T4) Baseline and periodically during chronic octreotide; periodically with somatropin Pituitary Hormone Agents

—

Toxic / critical —

Thyroid function in infants given potassium iodide Checked in babies under 1 month who take KI; pregnant or breastfeeding women are checked by a doctor if repeat dosing is needed Thyroid Agents

—

Toxic / critical —

Triglycerides Clomiphene: before starting, and periodically with pre-existing or family history of hyperlipidemia Selective Estrogen Receptor Modulators (SERMs)

—

Toxic / critical —

Trough Draw just before the next dose Aminoglycosides

Therapeutic < 2 mcg/mL for gentamicin/tobramycin (conventional; < 1 with extended-interval dosing)

Toxic / critical > 2 mcg/mL (gentamicin, tobramycin)

Trough Draw before the 4th dose Vancomycin (Glycopeptide)

Therapeutic 10–20 mg/L (modern AUC/MIC 400–600)

Toxic / critical Trough > 15 mg/L with AUC > 650 mg·h/L → highest AKI risk

TSH Periodic; titrate the dose to the TSH goal (recheck 6–8 weeks after any change) Thyroid Agents

Normal range 0.4–4.5 mIU/L

Toxic / critical —

TSH (thyroid function) Baseline & periodically — amiodarone is iodine-rich (hypo- or hyperthyroidism) Antiarrhythmics

Normal range 0.4–4.5 mU/L

Toxic / critical —

Uric acid Monitor in gout-prone patients Thiazide Diuretics

Normal range Typically < 6.8 mg/dL; hyperuricemia usually > 7 mg/dL (men) or > 6 mg/dL (women)

Toxic / critical Hyperuricemia → gout flare

Uric acid (bempedoic acid, niacin) As clinically indicated; bempedoic acid raises it within the first 4 weeks Other Lipid-Lowering Agents

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Toxic / critical —

Uterine activity, fetal heart rate and cervical change (dinoprostone; misoprostol in labor) Continuously while the prostaglandin is in place and until it is removed Uterotonics

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Toxic / critical —

Valproic acid level Trough; also monitor LFTs, ammonia, and platelets Anticonvulsants

Therapeutic 50–100 mcg/mL

Toxic / critical > 100 mcg/mL — dose-related effects such as thrombocytopenia (risk rises above 110–135); CNS dysfunction (tremor, agitation) at ≥ 180, which can progress to coma

Vision and hearing Ask about sudden changes during therapy PDE5 inhibitors

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Toxic / critical —

The middle column is tagged Therapeutic (a drug level you titrate to) or Normal range (a baseline you monitor). A dash means that side doesn't apply. Trough vs. peak timing matters — draw as noted. See each class page for the full monitoring plan.