Chlorthalidone

Diuretics such as chlorthalidone are indicated in the management of hypertension either as the sole therapeutic agent or to enhance the effect of other antihypertensive drugs in the more severe forms of hypertension.

Chlorthalidone is indicated as adjunctive therapy in edema associated with congestive heart failure, hepatic cirrhosis, and corticosteroid and estrogen therapy.

Chlorthalidone has also been found useful in edema due to various forms of renal dysfunction, such as nephrotic syndrome, acute glomerulonephritis, and chronic renal failure.

Therapy should be initiated with the lowest possible dose. This dose should be titrated according to individual patient response to gain maximal therapeutic benefit while maintaining lowest dosage possible. A single dose given in the morning with food is recommended; divided daily doses are unnecessary.

The following adverse reactions have been observed, but there is not enough systematic collection of data to support an estimate of their frequency.

Whenever adverse reactions are moderate or severe, chlorthalidone dosage should be reduced or therapy withdrawn.

Chlorthalidone may add to or potentiate the action of other antihypertensive drugs. Potentiation occurs with ganglionic peripheral adrenergic blocking drugs.

Medication such as digitalis may also influence serum electrolytes. Warning signs, irrespective of cause, are: dryness of mouth, thirst, weakness, lethargy, drowsiness, restlessness, muscle pains or cramps, muscular fatigue, hypotension, oliguria, tachycardia, and gastrointestinal disturbances such as nausea and vomiting.

Insulin requirements in diabetic patients may be increased, decreased, or unchanged. Higher dosage of oral hypoglycemic agents may be required. Latent diabetes mellitus may become manifest during chlorthalidone administration.

Chlorthalidone and related drugs may increase the responsiveness to tubocurarine.

Chlorthalidone and related drugs may decrease arterial responsiveness to norepinephrine. This diminution is not sufficient to preclude effectiveness of the pressor agent for therapeutic use.

Chlorthalidone is an oral antihypertensive/diuretic. It is a monosulfamyl diuretic that differs chemically from thiazide diuretics in that a double-ring system is incorporated in its structure. It is 2-Chloro-5(1- hydroxy-3-oxo-1-isoindolinyl) benzenesulfonamide with the following structural formula:

Molecular Formula: C₁₄H₁₁ClN₂O₄S   Molecular Weight: 338.76

Chlorthalidone, USP is practically insoluble in water, in ether, and in chloroform; soluble in methanol; slightly soluble in ethanol.

Chlorthalidone tablets are available containing either 25 mg or 50 mg of chlorthalidone, USP and the following inactive ingredients: microcrystalline cellulose, lactose monohydrate, povidone, sodium starch glycolate, D&C Yellow No. 10, magnesium stearate. The 50 mg Tablets also contain FD&C Blue No. 1.

FDA approved dissolution specification differs from that of the USP.