Overview
DESCRIPTION Chlorthalidone, USP 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: C 14 H 11 ClN 2 O 4 S Molecular weight: 338.
Mechanism of Action
CLINICAL PHARMACOLOGY Chlorthalidone is an oral diuretic with prolonged action (48-72 hours) and low toxicity. The major portion of the drug is excreted unchanged by the kidneys. The diuretic effect of the drug occurs in approximately 2.6 hours and continues for up to 72 hours. The mean half-life following a 50 to 200 mg dose is 40 hours. In the first order of absorption, the elimination half-life is 53 hours following a 50 mg dose, and 60 hours following a 100 mg dose. Approximately 75 percent of the drug is bound to plasma proteins, 58 percent of the drug being bound to albumin. This is caused by an increased affinity of the drug to erythrocyte carbonic anhydrase. Non renal routes of elimination have yet to be clarified.
Indications
- INDICATIONS AND USAGE 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.
Common Doses
- 25 mg
- 50 mg
- 100 mg
- 200 mg
Dosage
DOSAGE AND ADMINISTRATION 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. Hypertension Initiation: Therapy, in most patients, should be initiated with a single daily dose of 25 mg. If the response is insufficient after a suitable trial, the dosage may be increased to a single daily dose of 50 mg.
Contraindications
- CONTRAINDICATIONS Anuria. Known hypersensitivity to chlorthalidone or other sulfonamide-derived drugs.
Side Effects
- ADVERSE REACTIONS The following adverse reactions have been observed, but there is not enough systematic collection of data to support an estimate of their frequency. Gastrointestinal System Reactions: anorexia, gastric irritation, nausea, vomiting, cramping, diarrhea, constipation, jaundice (intrahepatic cholestatic jaundice), pancreatitis. Central Nervous System Reactions: dizziness, vertigo, paresthesias, headache, xanthopsia. Hematologic Reactions: leukopenia, agranulocytosis, thrombocytopenia, aplastic anemia.
Interactions
- Drug Interactions 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.