Chlortalidone: Long-Acting Thiazide-Like Diuretic
Chlortalidone (chlorthalidone) is a thiazide-like diuretic with a significantly longer duration of action (24–72 hours) compared to hydrochlorothiazide (6–12 hours). It is a first-line antihypertensive agent and was the diuretic used in major cardiovascular outcomes trials (ALLHAT).
Unlike true thiazides, chlortalidone binds to carbonic anhydrase and has a longer half-life (~50 hours), providing more sustained 24-hour blood pressure control including nocturnal blood pressure.
Mechanism of Action
Chlortalidone inhibits the Na+/Cl– cotransporter in the distal convoluted tubule, reducing sodium and water reabsorption and increasing urinary output. Chronic antihypertensive effect is primarily due to reduced peripheral vascular resistance rather than diuresis alone.
Indications & Use
Hypertension (first-line, especially in the elderly and Black patients), oedema due to heart failure or renal/hepatic disease, prevention of kidney stones (hypercalciuria), diabetes insipidus (nephrogenic).
Dosage
Hypertension: 12.5–25 mg once daily. Oedema: 25–100 mg/day or every other day. Lower doses recommended in elderly. Monitor electrolytes and renal function at baseline and after dose changes.
Side Effects
Common: hyponatraemia, hypokalaemia, hyperuricaemia (gout precipitation), hyperglycaemia, hyperlipidaemia (mild). Rare but serious: severe hyponatraemia, skin photosensitivity, thrombocytopenia.
Drug Interactions
NSAIDs: blunt diuretic effect. Lithium: increases toxicity (reduced renal clearance). ACE inhibitors/ARBs: additive hypotension (first dose). Digoxin: hypokalaemia increases toxicity risk. Antidiabetics: dose adjustment may be needed.
Contraindications
Anuria, severe renal impairment (GFR <30), severe hepatic failure, refractory hyponatraemia or hypokalaemia, hypersensitivity to sulfonamide derivatives.
Frequently Asked Questions
Is chlortalidone better than hydrochlorothiazide?
Most evidence supports chlortalidone for superior 24-hour blood pressure control and better cardiovascular outcomes (ALLHAT trial). Many guidelines now prefer chlortalidone over HCTZ for hypertension treatment.
How often should electrolytes be checked?
Check before starting, then at 4 weeks and after dose changes. In stable patients on long-term therapy, annual monitoring is generally sufficient.
Can chlortalidone worsen diabetes?
Chlortalidone can elevate blood glucose. In patients with diabetes or pre-diabetes, glucose monitoring should be intensified and antidiabetic therapy adjusted if needed.
References
- ALLHAT Trial investigators
- ESC Hypertension Guidelines 2023
- EMA product information chlortalidone
Medical Disclaimer: This information is for educational purposes only and does not replace professional medical advice.