Hydrochlorothiazide

# Hydrochlorothiazide ## Overview Thiazide diuretic; inhibits sodium-chloride cotransporter in distal convoluted tubule. Decreases reabsorption of sodium, chloride, and water. Also reduces peripheral vascular resistance. ## Primary Indications - Hypertension (alone or in combination) - Edema (e.g., heart failure, hepatic cirrhosis, nephrotic syndrome) - Nephrogenic diabetes insipidus (off-label) ## Adult Dosing - **Hypertension:** 12.5–25 mg once daily; max 50 mg/day in divided doses (usually 25 mg BID). Higher doses rarely add benefit but increase toxicity. - **Edema:** 25–100 mg once daily or intermittently; usual range 25–50 mg/day. - **Nephrogenic diabetes insipidus:** 25–50 mg once daily. ## Pediatric Dosing - **Hypertension:** - Children ≥1 month: 0.5–1 mg/kg once daily; max 2 mg/kg/day (or 50 mg/day total, whichever is lower). - Adolescents: 12.5–25 mg once daily; max 50 mg/day. - **Edema:** 1–2 mg/kg once daily or every other day; max 2 mg/kg/day (50 mg/day). - *Note: Dosing may vary by local protocol; adjust based on response.* ## Dose Adjustments - **Renal impairment:** Avoid if CrCl <30 mL/min (ineffective; risk of electrolyte disturbances). - **Hepatic impairment:** Use with caution; risk of fluid/electrolyte imbalances. - **Elderly:** Start at lowest dose (e.g., 12.5 mg) to avoid hypotension and electrolyte disturbances. ## Contraindications - Anuria - Severe renal impairment (CrCl <30 mL/min) - Hypersensitivity to hydrochlorothiazide or sulfonamide-derived drugs (cross-sensitivity risk – though rare) - Hypercalcemia - Untreated Addison’s disease (relative) ## Adverse Effects - **Common:** Hypokalemia, hyponatremia, hypomagnesemia, hyperuricemia, hyperglycemia, hyperlipidemia - **Less common but serious:** Orthostatic hypotension, volume depletion, acute pancreatitis, photosensitivity, sulfonamide-like reactions (e.g., Stevens-Johnson syndrome) - **Electrolytes:** Monitor K+, Na+, Mg²+, Ca²+ (mild hypercalcemia possible) - **Metabolic:** May worsen diabetes; increase uric acid and calcium ## Key Drug Interactions - **NSAIDs (especially indomethacin):** Reduced diuretic and antihypertensive effect; increased renal impairment risk. - **Lithium:** Decreased renal clearance → lithium toxicity. - **Digoxin:** Hypokalemia increases digoxin toxicity. - **Corticosteroids/amphotericin B:** Additive hypokalemia. - **Antidiabetic agents:** Thiazides may reduce glucose tolerance; monitor glycemic control. - **Cholestyramine/colestipol:** Reduce absorption; separate by ≥4 hours. ## Monitoring - Blood pressure, serum electrolytes (K+, Na+, Mg²+, Ca²+), renal function, uric acid - Glucose and lipids periodically (long-term) - Signs of hypokalemia: weakness, cramps, arrhythmias - Volume status in elderly/frail ## Clinical Pearls - **Hypertension:** Often used in low dose as add-on to ACEi/ARB; combination products reduce pill burden. - **Hypokalemia prevention:** Use with potassium-sparing diuretic or ensure dietary potassium intake. - **Nocturia:** Avoid bedtime dosing; administer early in day. - **Pregnancy:** Avoid (potential fetal/neonatal effects); use only if clearly needed. - **Sulfa allergy:** Reassess—true cross-reactivity is low but caution advised if history of severe sulfonamide hypersensitivity. - **Chlorthalidone:** Often preferred over HCTZ in hypertension trials for longer duration and better CV outcomes (though not universal). --- *Disclaimer: This information is for educational purposes and does not replace current, authoritative prescribing information. Always verify dosing, contraindications, and interactions with the latest drug monograph or clinical guidelines.*