Hydrochlorothiazide

Hydrochlorothiazide primarily acts on the distal convoluted tubule of the nephron, inhibiting the sodium-chloride symporter. This prevents the reabsorption of sodium and chloride ions, leading to increased excretion of water, sodium, chloride, and potassium. Its antihypertensive effect is also mediated by reducing peripheral vascular resistance through unknown mechanisms.

Adult

Hypertension: Initially 12.5 mg to 25 mg orally once daily. May be increased to 50 mg once daily. Edema: Initially 25 mg to 100 mg orally once daily or intermittently.

Pediatric

Hypertension/Edema (children >6 months): 0.5-1 mg/kg/day orally once daily or divided BID; Max 50 mg/day.

Renal adjustment

CrCl 30-80 mL/min: No dosage adjustment generally needed, but monitor closely. CrCl <30 mL/min: Not effective as a diuretic; avoid use. Loop diuretics are preferred.

Hepatic adjustment

Use with caution in patients with impaired hepatic function or progressive liver disease, as minor fluid and electrolyte alterations may precipitate hepatic coma. No specific dose adjustment guidelines exist, but lower doses may be considered.

Geriatric

Start at the lower end of the dosing range (e.g., 12.5 mg once daily) due to potential for decreased renal function and increased sensitivity to diuretic effects and electrolyte disturbances. Monitor electrolytes closely.

Max dose

25 mg/day (hypertension, per KDT); 100 mg/day (edema)

• Anuria
• Hypersensitivity to hydrochlorothiazide or other sulfonamide-derived drugs
• Severe renal impairment (CrCl <30 mL/min)
• Electrolyte imbalance (e.g., severe hyponatremia, hypokalemia)
• hypersensitive to sulfonamides
• sulfonamide hypersensitivity
• Gout
• Pregnancy
• Toxaemia of pregnancy