Label: CHLORTHALIDONE tablet

Usage in Pregnancy

The routine use of diuretics in an otherwise healthy woman is inappropriate and exposes mother and fetus to unnecessary hazard. Diuretics do not prevent development of toxemia of pregnancy, and there is no satisfactory evidence that they are useful in the treatment of developed toxemia. Edema during pregnancy may arise from pathologic causes or from the physiologic and mechanical consequences of pregnancy. Chlorthalidone is indicated in pregnancy when edema is due to pathologic causes, just as it is in the absence of pregnancy (however, see PRECAUTIONS, below). Dependent edema in pregnancy, resulting from restriction of venous return by the expanded uterus, is properly treated through elevation of the lower extremities and use of support hose; use of diuretics to lower intravascular volume in this case is illogical and unnecessary. There is hypervolemia during normal pregnancy that is harmful to neither the fetus nor the mother (in the absence of cardiovascular disease), but that is associated with edema, including generalized edema, in the majority of pregnant women. If this edema produces discomfort, increased recumbency will often provide relief. In rare instances, this edema may cause extreme discomfort that is not relieved by rest. In these cases, a short course of diuretics may provide relief and be appropriate.

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.

Information for Patients

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, or (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.

Laboratory Tests

Periodic determination of serum electrolytes to detect possible electrolyte imbalance should be performed at appropriate intervals.

All patients receiving chlorthalidone should be observed for clinical signs of fluid or electrolyte imbalance: namely, hyponatremia, hypochloremic alkalosis, and hypokalemia. Serum and urine electrolyte determinations are particularly important when the patient is vomiting excessively or receiving parenteral fluids.

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. 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.

Drug/Laboratory Test Interactions

Chlorthalidone and related drugs may decrease serum PBI levels without signs of thyroid disturbance.

Carcinogenesis, Mutagenesis, Impairment of Fertility

No information is available.

Pregnancy

Nursing Mothers

Thiazides are excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from chlorthalidone, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use

Safety and effectiveness in children have not been established.

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. If additional control is required, the dosage of chlorthalidone may be increased to 100 mg once daily or a second antihypertensive drug (step 2 therapy) may be added. Dosage above 100 mg daily usually does not increase effectiveness. Increases in serum uric acid and decreases in serum potassium are dose-related over the 25 to 100 mg/day range.

Maintenance: Maintenance doses may be lower than initial doses and should be adjusted according to individual patient response. Effectiveness is well sustained during continued use.

Edema

Initiation: Adults, initially 50 to 100 mg daily, or 100 mg on alternate days. Some patients may require 150 to 200 mg at these intervals or up to 200 mg daily. Dosages above this level, however, do not usually produce a greater response.

Maintenance: Maintenance doses may often be lower than initial doses and should be adjusted according to individual patient response. Effectiveness is well sustained during continued use.