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: C14 H11ClN2 O4 S

Molecular weight: 338.76

Chlorthalidone, USP is white to yellowish-white, crystalline powder that melts at a temperature 216°C to 222°C, with decomposition. It is practically insoluble in water, in ether, and in chloroform; soluble in methanol; slightly soluble in alcohol.

Chlorthalidone tablets, USP are available containing either 25 mg or 50 mg of chlorthalidone USP and the following inactive ingredients: colloidal silicon dioxide, corn starch,microcrystalline cellulose, pregelatinized starch, sodium starch glycolate and stearic acid.Additionally 25 mg tablet contain ferric oxide yellow.

Chlorthalidone is an oral diuretic with prolonged action (48 to 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. Nonrenal routes of elimination have yet to be clarified. Data are not available regarding percentage of dose as unchanged drug and metabolites, concentration of the drug in body fluids, degree of uptake by a particular organ or in the fetus, or passage across the blood-brain barrier.

The drug produces copious diuresis with greatly increased excretion of sodium and chloride. At maximal therapeutic dosage, chlorthalidone is approximately equal in its diuretic effect to comparable maximal therapeutic doses of benzothiadiazine diuretics. The site of action appears to be the cortical diluting segment of the ascending limb of Henle's loop of the nephron.

Diuretics such as chlorthalidone tablets, USP 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 tablets, USP are indicated as adjunctive therapy in edema associated with congestive heart failure, hepatic cirrhosis, and corticosteroid and estrogen therapy.

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

Anuria.

Known hypersensitivity to chlorthalidone or other sulfonamide-derived drugs.

Chlorthalidone should be used with caution in severe renal disease. In patients with renal disease, chlorthalidone or related drugs may precipitate azotemia. Cumulative effects of the drug may develop in patients with impaired renal function.

Chlorthalidone should be used with caution in patients with impaired hepatic function or progressive liver disease, since minor alterations of fluid and electrolyte balance may precipitate hepatic coma.

Sensitivity reactions may occur in patients with a history of allergy or bronchial asthma.

The possibility of exacerbation or activation of systemic lupus erythematosus has been reported with thiazide diuretics, which are structurally related to chlorthalidone. However, systemic lupus erythematosus has not been reported following chlorthalidone administration.

General

Hypokalemia may develop with chlorthalidone as with any other diuretic, especially with brisk diuresis when severe cirrhosis is present or during concomitant use of corticosteroids or ACTH.

Interference with adequate oral electrolyte intake will also contribute to hypokalemia. Digitalis therapy may exaggerate metabolic effects of hypokalemia especially with reference to myocardial activity.

Any chloride deficit is generally mild and usually does not require specific treatment except under extraordinary circumstances (as in liver disease or renal disease). Dilutional hyponatremia may occur in edematous patients in hot weather, appropriate therapy is water restriction, rather than administration of salt except in rare instances when the hyponatremia is life threatening. In actual salt depletion, appropriate replacement is the therapy of choice.

Hyperuricemia may occur or frank gout may be precipitated in certain patients receiving chlorthalidone.

Thiazide-like diuretics have been shown to increase the urinary excretion of magnesium; this may result in hypomagnesemia.

The antihypertensive effects of the drug may be enhanced in the post-sympathectomy patient.

If progressive renal impairment becomes evident, as indicated by a rising nonprotein nitrogen or blood urea nitrogen, a careful reappraisal of therapy is necessary with consideration given to withholding or discontinuing diuretic therapy.

Calcium excretion is decreased by thiazide-like drugs. Pathological changes in the parathyroid gland with hypercalcemia and hypophosphatemia have been observed in few patients on thiazide therapy. The common complications of hyperparathyroidism such as renal lithiasis, bone resorption and peptic ulceration have not been seen.

Patients should inform their physician if they have:

1. had an allergic reaction to chlorthalidone or other diuretics or have asthma
2. kidney disease
3. liver disease
4. gout
5. systemic lupus erythematosus
6. been taking other drugs such as cortisone, digitalis, lithium carbonate, or drugs for diabetes.

Patients should be cautioned to contact their physician if they experience any of the following symptoms of potassium loss: excess thirst, tiredness, drowsiness, restlessness, muscle pains or cramps, nausea, vomiting, or increased heart rate or pulse.

Patients should also be cautioned that taking alcohol can increase the chance of dizziness occurring.

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.

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.

Dermatologic-Hypersensitivity Reactions: purpura, photosensitivity, rash, urticaria, necrotizing angiitis (vasculitis, cutaneous vasculitis), Lyell's syndrome (toxic epidermal necrolysis).

Cardiovascular Reactions: orthostatic hypotension may occur and may be aggravated by alcohol, barbiturates, or narcotics.

Other Adverse Reactions: hyperglycemia, glycosuria, hyperuricemia, muscle spasm, weakness, restlessness, impotence.

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

Symptoms of acute overdosage include nausea, weakness, dizziness, and disturbances of electrolyte balance. The oral LD50 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.

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.

Chlorthalidone Tablets, USP are available containing 25 mg or 50 mg of Chlorthalidone, USP.

The 25 mg tablets are light yellow, round, flat faced beveled edged unscored tablets debossed with "Z25" on one side of the tablet and plain on other side. They are available as follows:

NDC 68382-970-01 in bottle of 100 tablets

NDC 68382-970-10 in bottle of 1000 tablets

The 50 mg tablets are white to off white, round, flat faced beveled edged, scored tablets debossed with 'Z' and '50' on either side of score line on one side of the tablet and plain on the other side.  They are available as follows:

NDC 68382-971-01 in bottle of 100 tablets

NDC 68382-971-10 in bottle of 1000 tablets

Store at 20° to 25°C (68° to 77°F). [See USP for Controlled Room Temperature.]

Protect from light.

Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.

Biochemical studies in animals have suggested reasons for the prolonged effect of chlorthalidone. Absorption from the gastrointestinal tract is slow due to its low solubility. After passage to the liver, some of the drug enters the general circulation, while some is excreted in the bile, to be reabsorbed later. In the general circulation, it is distributed widely to the tissue, but is taken up in highest concentrations by the kidneys, where amounts have been found 72 hours after ingestion, long after it has disappeared from other tissues. The drug is excreted unchanged in the urine.

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

This product's package insert may have been updated. For current package insert, please visit www.zydususa.com

Manufactured by:

Zydus Lifesciences Ltd.

Ahmedabad, India.

Distributed by:

Zydus Pharmaceuticals (USA) Inc.

Pennington, NJ 08534

Rev.: 08/22

NDC 68382-970-01

Chlorthalidone tablets USP ,25 mg

Rx only

100 tablets

Zydus

NDC 68382-971-01

Chlorthalidone tablets USP ,50 mg

Rx only

100 tablets

Zydus