HYDROCHLOROTHIAZIDE Edema during pregnancy may arise from patho­ irritability). Hypokalemia may be avoided or treated logic causes or from the physiologic and mechanical by use of potassium sparing diuretics or potassium TABLETS, USP consequences of pregnancy. Thiazides are indicated supplements such as foods with a high potassium 12.5 mg, 25 mg and 50 mg in pregnancy when edema is due to pathologic content. causes, just as they are in the absence of pregnan­ Although any chloride deficit is generally mild and cy (see PRECAUTIONS: Pregnancy). Dependent usually does not require specific treatment except edema in pregnancy, resulting from restriction of under extraordinary circumstances (as in liver dis­ DESCRIPTION: Hydrochlorothiazide is a diuretic venous return by the gravid uterus, is properly treat­ ease or renal disease), chloride replacement may and antihypertensive. It is the 3,4-dihydro derivative ed through elevation of the lower extremities and be required in the treatment of metabolic alkalosis. of chlorothiazide. It is chemically designated as 6­ use of support stockings. Use of diuretics to lower Dilutional hyponatremia may occur in edematous chloro-3,4-dihydro-2 H-1,2,4-benzothiadiazine-7-sul­ intravascular volume in this instance is illogical and patients in hot weather; appropriate therapy is water fonamide 1,1-dioxide and has the following structural unnecessary. During normal pregnancy there is restriction, rather than administration of salt, except formula: hypervolemia which is not harmful to the fetus or the in rare instances when the hyponatremia is life mother in the absence of cardiovascular disease. threatening. In actual salt depletion, appropriate However, it may be associated with edema, rarely replacement is the therapy of choice. generalized edema. If such edema causes discom­ fort, increased recumbency will often provide relief. Hyperuricemia may occur or acute gout may be Rarely this edema may cause extreme discomfort precipitated in certain patients receiving thiazides. which is not relieved by rest. In these instances, a In diabetic patients dosage adjustments of insulin short course of diuretic therapy may provide relief or oral hypoglycemic agents may be required. HCTZT:R2 and be appropriate. Hyper glycemia may occur with thiazide diuretics. Thus latent diabetes mellitus may become manifest C7H8ClN3O4S2 M.W. 297.74 CONTRAINDICATIONS: Anuria. during thiazide therapy. Hydrochlorothiazide, USP is a white, or practically Hypersensitivity to this product or to other sulfon­ The antihypertensive effects of the drug may be white, crystalline powder which is slightly soluble in amide-derived drugs. enhanced in the post-sympathectomy patient. water, freely soluble in sodium hydroxide solution, in WARNINGS: Use with caution in severe renal dis­ If progressive renal impairment becomes evi­ n-butylamine, and in dimethylformamide; sparingly ease. In patients with renal disease, thiazides may dent, consider withholding or discontinuing diuretic soluble in methanol; insoluble in ether, in chloroform, precipitate azotemia. Cumulative effects of the drug therapy. and in dilute mineral acids. Each tablet for oral may develop in patients with impaired renal function. Thiazides have been shown to increase the uri­ administration contains 12.5 mg, 25 mg or 50 mg Thiazides should be used with caution in patients nary excretion of magnesium; this may result in hydrochlorothiazide, USP. In addition, each tablet with impaired hepatic function or progressive liver hypomagnesemia. contains the following inactive ingredients: colloidal disease, since minor alterations of fluid and elec­ Thiazides may decrease urinary calcium excre­ silicon dioxide, magnesium stearate, microcrystalline trolyte balance may precipitate hepatic coma. cellulose, pregelatinized starch, and sodium lauryl tion. Thiazides may cause intermittent and slight ele­ Thiazides may add to or potentiate the action of sulfate. vation of serum calcium in the absence of known other antihypertensive drugs. disorders of calcium metabolism. Marked hypercal­ CLINICAL PHARMACOLOGY: The mechanism of Sensitivity reactions may occur in patients with or cemia may be evidence of hidden hyperparathy­ the antihypertensive effect of thiazides is unknown. without a history of allergy or bronchial asthma. roidism. Thiazides should be discontinued before Hydrochlorothiazide does not usually affect normal The possibility of exacerbation or activation of sys­ carrying out tests for parathyroid function. blood pressure. temic lupus erythematosus has been reported. Increases in cholesterol and triglyceride levels Hydrochlorothiazide affects the distal renal tubular Lithium generally should not be given with diuret­ may be associated with thiazide diuretic therapy. mechanism of electrolyte reabsorption. At maximal ics (see PRECAUTIONS: Drug Interactions). Laboratory Tests: Periodic determination of serum therapeutic dosage all thiazides are approximately electrolytes to detect possible electrolyte imbalance equal in their diuretic efficacy. Acute Myopia and Secondary Angle-Closure Glaucoma: Hydrochlorothiazide, a sulfonamide, should be done at appropriate intervals. Hydrochlorothiazide increases excretion of sodi­ can cause an idiosyncratic reaction, resulting in Drug Interactions: When given concurrently the um and chloride in approximately equivalent acute transient myopia and acute angle-closure following drugs may interact with thiazide diuretics. amounts. Natriuresis may be accompanied by some glaucoma. Symptoms include acute onset of loss of potassium and bicarbonate. Alcohol, Barbiturates, or Narcotics: Potentiation decreased visual acuity or ocular pain and typically of orthostatic hypotension may occur. After oral use diuresis begins within 2 hours, occur within hours to weeks of drug initiation. Antidiabetic Drugs (Oral Agents and Insulin): peaks in about 4 hours and lasts about 6 to 12 Untreated acute angle-closure glaucoma can lead to Dosage adjustment of the antidiabetic drug may be hours. permanent vision loss. The primary treatment is to required. Pharmacokinetics and Metabolism: Hydro ­ discontinue hydrochlorothiazide as rapidly as possi­ chlorothiazide is not metabolized but is eliminated ble. Prompt medical or surgical treatments may Other Antihypertensive Drugs: Additive effect or rapidly by the kidney. When plasma levels have been need to be considered if the intraocular pressure potentiation. followed for at least 24 hours, the plasma half-life remains uncontrolled. Risk factors for developing Cholestyramine and Colestipol Resins: has been observed to vary between 5.6 and 14.8 acute angle-closure glaucoma may include a history Absorption of hydrochlorothiazide is impaired in the hours. At least 61% of the oral dose is eliminated of sulfonamide or penicillin allergy. presence of anionic exchange resins. Single doses unchanged within 24 hours. Hydro chlorothiazide of either cholestyramine or colestipol resins bind the crosses the placental but not the blood-brain barrier PRECAUTIONS: General: All patients receiving hydrochlorothiazide and reduce its absorption from and is excreted in breast milk. diuretic therapy should be observed for evidence of the gastrointestinal tract by up to 85% and 43%, fluid or electrolyte imbalance: namely, hyponatrem­ respectively. INDICATIONS AND USAGE: Hydrochlorothiazide ia, hypochloremic alkalosis, and hypokalemia. Corticosteroids, ACTH: Intensified electrolyte tablets are indicated as adjunctive therapy in edema Serum and urine electrolyte determinations are par­ depletion, particularly hypokalemia. associated with congestive heart failure, hepatic cir­ ticularly important when the patient is vomiting rhosis, and corticosteroid and estrogen therapy. excessively or receiving parenteral fluids. Warning Pressor Amines (e.g., Norepinephrine): Possible Hydrochlorothiazide tablets have also been found signs or symptoms of fluid and electrolyte imbal­ decreased response to pressor amines but not suffi­ useful in edema due to various forms of renal dys­ ance, irrespective of cause, include dryness of cient to preclude their use. function such as nephrotic syndrome, acute mouth, thirst, weakness, lethargy, drowsiness, rest­ Skeletal Muscle Relaxants, Nondepolarizing glomerulonephritis, and chronic renal failure. lessness, confusion, seizures, muscle pains or (e.g., Tubocurarine): Possible increased respon­ Hydrochlorothiazide tablets are indicated in the cramps, muscular fatigue, hypotension, oliguria, siveness to the muscle relaxant. management of hypertension either as the sole ther­ tachycardia, and gastrointestinal disturbances such Lithium: Generally should not be given with diuret­ apeutic agent or to enhance the effectiveness of as nausea and vomiting. ics. Diuretic agents reduce the renal clearance of other antihypertensive drugs in the more severe Hypokalemia may develop, especially with brisk lithium and add a high risk of lithium toxicity. Refer to forms of hypertension. diuresis, when severe cirrhosis is present or after the package insert for lithium preparations before Use in Pregnancy: Routine use of diuretics during prolonged therapy. use of such preparations with hydrochlorothiazide. normal pregnancy is inappropriate and exposes Interference with adequate oral electrolyte intake Non-Steroidal Anti-Inflammatory Drugs: In mother and fetus to unnecessary hazard. Diuretics will also contribute to hypokalemia. Hypokalemia some patients, the administration of a non-steroidal do not prevent development of toxemia of