| Definition | Thiazide diuretic used as first-line therapy for hypertension; increases urinary sodium and water excretion. | Pharmacological Classification | Thiazide diuretic; antihypertensive agent | Structural Formula | Empirical formula: C7H8ClN3O4S2 Structural class: benzothiadiazine derivative |
| Mechanism of Action | Blocks Na⁺/Cl⁻ cotransporter in distal convoluted tubule → ↑ Na⁺/water excretion, ↓ plasma volume, ↓ BP. | Indications | • Hypertension (first-line) • Edema (HF, cirrhosis, nephrotic syndrome) • Kidney stones (↓ Ca²⁺ excretion) |
Monitoring Parameters | • BP, HR • Serum electrolytes (K⁺, Na⁺, Mg²⁺) • Renal function (SCr, BUN) • Uric acid, glucose (risk ↑) |
| Pharmacokinetics | Onset 2h, peak 4-6h, duration 12h PO absorption 60–70% Renal excretion T1/2 ~6-15h |
Pharmacodynamics | ↓ total peripheral resistance (chronic) ↓ preload & blood volume |
Adverse Drug Reactions | • Electrolyte imbalance (↓K⁺, ↓Na⁺, ↓Mg²⁺) • Dizziness, weakness • Rash, photosensitivity • Rare: pancreatitis |
| Dosage | Adults HTN: 12.5–25 mg PO daily (max 50 mg/day) Edema: 25–100 mg/day divided Pediatrics: 1–2 mg/kg/day (max 37.5 mg/day) |
Contraindications | • Sulfonamide allergy (relative) • Anuria • Severe renal failure • Hypokalemia / hyponatremia |
Drug–Drug Interaction | • NSAIDs ↓ diuretic effect • ACEi/ARBs ↑ hypotension / renal risk • Lithium ↑ toxicity • Digoxin ↑ arrhythmia with ↓K⁺ |
| Clinical Tips | • Pair with ACEi/ARB for synergistic BP control • Use low doses – higher doses ↑ metabolic effects without extra BP benefit • Monitor BP effect after 2–4 weeks |
Toxicity | • Hypokalemia, hyponatremia, hypomagnesemia • Hyperuricemia; gout flare • Hyperglycemia • Photosensitivity |
Counselling | • Take morning to avoid nocturia • Monitor electrolytes routinely • May ↑ uric acid → caution in gout • Use sunscreen due to photosensitivity |
