Chlorthalidone: Effects, Dosage & Side Effects
Chlorthalidone is a long-acting diuretic used to treat high blood pressure and fluid retention. It works by increasing the excretion of water and salt through the kidneys.
Things worth knowing about "Chlorthalidone"
Chlorthalidone is a long-acting diuretic used to treat high blood pressure and fluid retention. It works by increasing the excretion of water and salt through the kidneys.
What is Chlorthalidone?
Chlorthalidone is a thiazide-like diuretic (water pill) used in the treatment of high blood pressure (hypertension) and edema (fluid accumulation in body tissues). It is one of the oldest and most thoroughly studied antihypertensive medications, recommended as a first-line agent in many cardiology guidelines. Compared to other thiazide diuretics such as hydrochlorothiazide, chlorthalidone has a significantly longer duration of action – up to 72 hours.
Indications
Chlorthalidone is prescribed for:
- Arterial hypertension (high blood pressure)
- Edema caused by heart failure, liver disease, or kidney disorders
- Nephrolithiasis (kidney stones), particularly calcium-containing stones (off-label use)
- Nephrogenic diabetes insipidus (off-label use)
Mechanism of Action
Chlorthalidone inhibits the sodium-chloride cotransporter (NCC) in the distal tubule of the kidney. This reduces the reabsorption of sodium and chloride, leading to increased urinary excretion of water, sodium, potassium, and chloride. The resulting decrease in blood volume lowers blood pressure. With prolonged use, blood vessel walls also relax, further enhancing the antihypertensive effect.
Dosage
The dosage of chlorthalidone depends on the indication and the individual response of the patient:
- Hypertension: Typically 12.5 to 25 mg once daily, maximum 50 mg per day
- Edema: 25 to 50 mg daily, in some cases up to 100 mg daily (under medical supervision)
- It is recommended to take chlorthalidone in the morning to avoid sleep disturbances caused by frequent urination at night.
Side Effects
Like all medications, chlorthalidone may cause side effects. Common and clinically relevant side effects include:
- Hypokalemia (low potassium): Can cause muscle weakness, fatigue, and heart rhythm disturbances
- Hyponatremia (low sodium): May lead to dizziness, confusion, and nausea
- Hyperuricemia: Elevated uric acid levels, which can trigger gout attacks
- Hyperglycemia: Elevated blood sugar levels, particularly relevant for diabetic patients
- Elevated blood lipids (cholesterol, triglycerides)
- Headaches, muscle cramps, and increased sensitivity to sunlight
- In rare cases: Thrombocytopenia (low platelet count)
Contraindications
Chlorthalidone should not be used in patients with:
- Severe renal impairment (GFR below 30 ml/min)
- Severe hepatic impairment
- Hypersensitivity to sulfonamides or chlorthalidone itself
- Pregnancy (especially the first and second trimester) and breastfeeding
- Severe hypokalemia or hyponatremia
Drug Interactions
Chlorthalidone may interact with various medications:
- Digitalis preparations: Hypokalemia induced by chlorthalidone increases the risk of digitalis toxicity
- Lithium: Chlorthalidone may increase lithium blood levels
- NSAIDs (e.g., ibuprofen): May reduce the blood pressure-lowering effect
- Antidiabetic agents: Chlorthalidone may elevate blood glucose and interfere with antidiabetic therapy
References
- Whelton PK, et al. - 2017 ACC/AHA High Blood Pressure Clinical Practice Guideline. Journal of the American College of Cardiology. 2018;71(19):e127-e248.
- Musini VM, et al. - Pharmacotherapy for hypertension in adults 60 years or older. Cochrane Database of Systematic Reviews. 2019.
- Ernst ME, Moser M. - Use of diuretics in patients with hypertension. New England Journal of Medicine. 2009;361(22):2153-2164.
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