Chlorthalidone is a prescription drug used to treat high blood pressure (hypertension). Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems. It is also used to reduce extra salt and water in the body caused by conditions such as heart failure, liver disease, and kidney disease.
Chlorthalidone is a thiazide-type Diuretic- Antihypertensive, used for the treatment of hypertension. It may be used alone or in association with other antihypertensive agents. Chlortalidone is also indicated for adjunctive therapy of edema associated with: renal disease; congestive heart failure of mild to moderate degree (functional class II, Ill), when glomerular filtration rate is greater than 30 ml/min; ascites due to cirrhosis of the liver in stable patients; estrogen therapy; corticosteroid therapy.
Chlorthalidone inhibits the reabsorption of sodium and chloride in the distal renal tubule thus promoting water loss. The higher urine volume increases potassium loss. Little information is available on the absorption of the drug. Its long elimination half-life and clinical experience place it as a long-acting thiazide derivative. The longer-acting agents appear to cause increased potassium loss.
Although a mild diuretic, its combination with loop diuretics is particularly potent because the latter presents much more sodium chloride to the distal tubule.
The blood pressure lowering effects are initially due to volume reduction but the persisting effect includes other undetermined mechanisms that reduce peripheral resistance. A high salt intake reverses its antihypertensive effect.
The major portion of an absorbed dose of Chlorthalidone is excreted by the kidneys with an elimination half life averaging 50 hours. Metabolism and hepatic excretion into the bile constitute a minor way of elimination. Within 120 hours, about 70% of the dose is excreted in the urine and in the feces, mainly in an unchanged form.
Ascites due to cirrhosis in stable patients (under close supervision) | Oedema due to nephrotic syndrome BY MOUTH Adult: Up to 50 mg daily Hypertension BY MOUTH Adult: 25 mg daily, dose to be taken in the morning, then increased if necessary to 50 mg daily Mild to moderate chronic heart failure BY MOUTH Adult: 25-50 mg daily, dose to be taken in the morning, then increased if necessary to 100-200 mg daily, reduce to lowest effective dose for maintenance Nephrogenic diabetes insipidus | Partial pituitary diabetes insipidus BY MOUTH Adult: Initially 100 mg twice daily, then reduced to 50 mg daily.
Other interactions: Patients with Special Diseases and Conditions in patients with impaired hepatic function or progressive liver disease, caution should be exercised since even minor alterations in fluid and electrolyte balance or of serum ammonia may precipitate hepatic coma. Treatment with thiazide diuretics should be initiated cautiously in postsympathectomy patients since the antihypertensive effects may be enhanced. A cautious dosage schedule should be adopted in patients with severe coronary or cerebral ateriosderosis.
Drug Interactions-
Antihypertensive Agents: Diuretics potentiate the action of curare derivatives and antihypertensive agents (e.g. guanethidine, methyldopa, beta-blockers, vasodilators, calcium antagonists, ACE inhibitors).
Digitalis: Thiazide-induced hypokalemia or hypomagnesemia may increase the likelihood of digitalis-induced cardiac arrhythmias (see also Precautions).
Corticosteroids: The hypokalemic effects of diuretics may be increased by corticosteroids, ACTH and amphotericin. Insulin and Oral Antidiabetic Agents: It may be necessary to adjust the dosage of insulin or oral antidiabetic agents in response to changes in glucose tolerance that Chlorthalidone may produce.
NSAIDs: Concomitant administration of certain NSAIDs (e.g. indomethacin) may weaken the diuretic and antihypertensive activity of thiazides, and there have been isolated reports of a deterioration of renal function in predisposed patients.
Curare Derivatives and Ganglionic Blocking Agents: Thiazides may increase responsiveness to curare derivatives and ganglionic blocking agents.
Allopurinol: Co-administration of thiazide diuretics may increase the incidence of hypersensitivity reactions to allopurinol.
Amantadine: Co-administration of thiazide diuretics may increase the risk of adverse effects from amantadine.
Antineoplastic Agents (e.g. cyclophosphamide, methotrexate): Concomitant use of thiazide diuretics may reduce renal excretion of cytotoxic agents and enhance the myelo suppressive effects. Anticholinergics (e.g. atropine, biperiden): The bioavailability of thiazide-type diuretics may be increased by anticholinergic agents, apparently due to a decrease in gastrointestinal motility and rate of gastric emptying.
Cholestyramine: Absorption of thiazide diuretics is decreased by cholestyramine, therefore a decrease in pharmacological effect may be expected.
Vitamin D: Concomitant use of thiazide diuretics may decrease urinary excretion of calcium, and co-administration of Vitamin D may potentiate the increase in serum calcium.
Cyclosporin: Concomitant treatment with diuretics may increase the risk of hyperuricemia and gout-type complications.
Calcium Salts: Concomitant use of thiazide-type diuretics may cause hypercalcemia by increasing tubular calcium reabsorption.
Diazoxide: Thiazide diuretics may enhance the hyperglycemic effect of diazoxide.
Allergic interstitial nephritis . Jaundice.
BREAST FEEDING The amount present in milk is too small to be harmful. Large doses may suppress lactation.
Symptoms of acute overdosage include nausea, weakness, dizziness, and disturbances of electrolyte balance. The oral LD 50 of the drug in the mouse and the rat is more than 25,000 mg/kg body weight. The minimum lethal dose (MLD) in humans has not been established. There is no specific antidote, but gastric lavage is recommended, followed by supportive treatment. Where necessary, this may include intravenous dextrose-saline with potassium, administered with caution.
Keep below 30°C temperature, away from light & moisture. Keep out of the reach of children.
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