CHLOROTHIAZIDE TABLETS, USP
mg and 500 mg
Rx Only
DESCRIPTION
Chlorothiazide is a diuretic and antihypertensive. It is 6- chloro-2 H -1,2,4-benzothiadiazine-7-sulfonamide 1, 1-dioxide. Its molecular formula is C7H6CIN3O4S2 and its structural formula is:
Chlorothiazide, USP is a white, or practically white crystalline compound with a molecular weight of 295.73 which is very slightly soluble in water, but readily soluble in dilute aqueous sodium hydroxide. It is soluble in urine to the extent of about 150 mg per 100 mL at pH 7.
Each tablet for oral administration contains either 250 mg or 500 mg of chlorothiazide and the following inactive ingredients: colloidal silicon dioxide, croscarmellose sodium-Type A, magnesium stearate, microcrystalline cellulose, sodium lauryl sulfate.
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CLINICAL PHARMACOLOGY
The mechanism of the antihypertensive effect of thiazides is unknown. Chlorothiazide does not usually affect normal blood pressure.
Chlorothiazide affects the distal renal tubular mechanism of electrolyte reabsorption. At maximal therapeutic dosages, all thiazides are approximately equal in their diuretic efficacy.
Chlorothiazide increases excretion of sodium and chloride in approximately equivalent amounts. Natriuresis may be accompanied by some loss of potassium and bicarbonate.
After oral use diuresis begins within 2 hours, peaks in about 4 hours, and lasts about 6 to 12 hours.
Pharmacokinetics and Metabolism
Chlorothiazide is not metabolized but is eliminated rapidly by the kidney. The plasma half-life of chlorothiazide is 45 to 120 minutes. After oral doses, 10 to 15 percent of the dose is excreted unchanged in the urine. Chlorothiazide crosses the placental but not the blood-brain barrier and is excreted in breast milk.
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