SPIRONOLACTONE and HYDROCHLOROTHIAZIDE TABLETS, USP
25 mg/25 mg

Spironolactone has been shown to be a tumorigen in chronic toxicity studies in rats (see PRECAUTIONS). Spironolactone and hydrochlorothiazide should be used only in those conditions described under INDICATIONS AND USAGE. Unnecessary use of this drug should be avoided.

Fixed-dose combination drugs are not indicated for initial therapy of edema or hypertension. Edema or hypertension requires therapy titrated to the individual patient. If the fixed combination represents the dosage so determined, its use may be more convenient in patient management. The treatment of hypertension and edema is not static but must be reevaluated as conditions in each patient warrant.

Each tablet of spironolactone and hydrochlorothiazide contains 25 mg of spironolactone, USP and 25 mg of hydrochlorothiazide, USP. Spironolactone, an aldosterone antagonist, is 17-hydroxy-7α-mercapto-3-oxo-17α-pregn-4-ene-21-carboxylic acid γ-lactone acetate and has the following structural formula, molecular formula, and molecular weight:

C₂₄H₃₂O₄S
M.W. = 416.59

Spironolactone is practically insoluble in water, soluble in alcohol, and freely soluble in benzene and in chloroform.

Hydrochlorothiazide, a diuretic and antihypertensive, is 6-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide 1,1-dioxide and has the following structural formula, molecular formula, and molecular weight:

C₇H₈ClN₃O₄S₂
M.W. = 297.75

Hydrochlorothiazide is slightly soluble in water and freely soluble in sodium hydroxide solution.

Each tablet for oral administration contains 25 mg of spironolactone and 25 mg of hydrochlorothiazide and the following inactive ingredients: colloidal silicon dioxide, D&C yellow #10 aluminum lake HT, FD&C yellow #6 aluminum lake HT, lactose, magnesium stearate, microcrystalline cellulose, menthol, peppermint oil, sodium lauryl sulfate, sodium starch glycolate and starch.

Spironolactone and hydrochlorothiazide is a combination of two diuretic agents with different but complementary mechanisms and sites of action, thereby providing additive diuretic and antihypertensive effects. Additionally, the spironolactone component helps to minimize the potassium loss characteristically induced by the thiazide component.

The diuretic effect of spironolactone is mediated through its action as a specific pharmacologic antagonist of aldosterone, primarily by competitive binding of receptors at the aldosterone-dependent sodium-potassium exchange site in the distal convoluted renal tubule. Hydrochlorothiazide promotes the excretion of sodium and water primarily by inhibiting their reabsorption in the cortical diluting segment of the distal renal tubule.

Spironolactone and hydrochlorothiazide is effective in significantly lowering the systolic and diastolic blood pressure in many patients with essential hypertension, even when aldosterone secretion is within normal limits.

Both spironolactone and hydrochlorothiazide reduce exchangeable sodium, plasma volume, body weight, and blood pressure. The diuretic and antihypertensive effects of the individual components are potentiated when spironolactone and hydrochlorothiazide are given concurrently.

Spironolactone is rapidly and extensively metabolized. Sulfur-containing products are the predominant metabolites and are thought to be primarily responsible, together with spironolactone, for the therapeutic effects of the drug. The following pharmacokinetic data were obtained from 12 healthy volunteers following the administration of 100 mg of spironolactone (as tablets) daily for 15 days. On the 15th day, spironolactone was given immediately after a low-fat breakfast and blood was drawn thereafter.

The pharmacological activity of spironolactone metabolites in man is not known. However, in the adrenalectomized rat the antimineralocorticoid activities of the metabolites C, TMS, and HTMS, relative to spironolactone, were 1.1, 1.28, and 0.32, respectively. Relative to spironolactone, their binding affinities to the aldosterone receptors in rat kidney slices were 0.19, 0.86, and 0.06, respectively.

In humans the potencies of TMS and 7-α-thiospironolactone in reversing the effects of the synthetic mineralocorticoid, fludrocortisone, on urinary electrolyte composition were 0.33 and 0.26, respectively, relative to spironolactone. However, since the serum concentrations of these steroids were not determined, their incomplete absorption and/or firstpass metabolism could not be ruled out as a reason for their reduced in vivo activities.

Spironolactone and its metabolites are more than 90% bound to plasma proteins. The metabolites are excreted primarily in the urine and secondarily in bile.

The effect of food on spironolactone absorption (two 100 mg spironolactone tablets) was assessed in a single dose study of 9 healthy, drug-free volunteers. Food increased the bioavailability of unmetabolized spironolactone by almost 100%. The clinical importance of this finding is not known.

Hydrochlorothiazide is rapidly absorbed following oral administration. Onset of action of hydrochlorothiazide is observed within one hour and persists for 6 to 12 hours. Hydrochlorothiazide plasma concentrations attain peak levels at one to two hours and decline with a half-life of four to five hours. Hydrochlorothiazide undergoes only slight metabolic alteration and is excreted in urine. It is distributed throughout the extracellular space, with essentially no tissue accumulation except in the kidney.

Spironolactone has been shown to be a tumorigen in chronic toxicity studies in rats (see PRECAUTIONS section). Spironolactone and hydrochlorothiazide tablets should be used only in those conditions described below. Unnecessary use of this drug should be avoided.

Spironolactone and Hydrochlorothiazide Tablets are Indicated for:

Spironolactone and hydrochlorothiazide tablets are contraindicated in patients with anuria, acute renal insufficiency, significant impairment of renal excretory function, or hyperkalemia, and in patients who are allergic to thiazide diuretics or to other sulfonamide-derived drugs. Spironolactone and hydrochlorothiazide may also be contraindicated in acute or severe hepatic failure.

Potassium supplementation, either in the form of medication or as a diet rich in potassium, should not ordinarily be given in association with spironolactone and hydrochlorothiazide therapy. Excessive potassium intake may cause hyperkalemia in patients receiving spironolactone and hydrochlorothiazide (see PRECAUTIONS: General). Spironolactone and hydrochlorothiazide should not be administered concurrently with other potassium-sparing diuretics. Spironolactone, when used with ACE inhibitors or indomethacin, even in the presence of a diuretic, has been associated with severe hyperkalemia. Extreme caution should be exercised when spironolactone and hydrochlorothiazide is given concomitantly with these drugs (see PRECAUTIONS: Drug Interaction).

Spironolactone and hydrochlorothiazide should be used with caution in patients with impaired hepatic function because minor alterations of fluid and electrolyte balance may precipitate hepatic coma.

Lithium generally should not be given with diuretics (see PRECAUTIONS: Drug Interactions).

Thiazides should be used with caution in severe renal disease. In patients with renal disease, thiazides may precipitate azotemia. Cumulative effects of the drug may develop in patients with impaired renal function.

Thiazides may add to or potentiate the action of other antihypertensive drugs.

Sensitivity reactions to thiazides may occur in patients with or without a history of allergy or bronchial asthma.

Sulfonamide derivatives, including thiazides, have been reported to exacerbate or activate systemic lupus erythematosus.

All patients receiving diuretic therapy should be observed for evidence of fluid or electrolyte imbalance, e.g., hypomagnesemia, hyponatremia, hypochloremic alkalosis, and hypokalemia or hyperkalemia.

Serum and urine electrolyte determinations are particularly important when the patient is vomiting excessively or receiving parenteral fluids. Warning signs or symptoms of fluid and electrolyte imbalance, irrespective of cause, include dryness of the mouth, thirst, weakness, lethargy, drowsiness, restlessness, muscle pains or cramps, muscular fatigue, hypotension, oliguria, tachycardia, and gastrointestinal disturbances such as nausea and vomiting. Hyperkalemia may occur in patients with impaired renal function or excessive potassium intake and can cause cardiac irregularities, which may be fatal. Consequently, no potassium supplement should ordinarily be given with spironolactone and hydrochlorothiazide.

Concomitant administration of potassium-sparing diuretics and ACE inhibitors or nonsteroidal anti-inflammatory drugs (NSAIDs), e.g., indomethacin, has been associated with severe hyperkalemia.

If hyperkalemia is suspected (warning signs include paresthesia, muscle weakness, fatigue, flaccid paralysis of the extremities, bradycardia and shock) an electrocardiogram (ECG) should be obtained. However, it is important to monitor serum potassium levels because mild hyperkalemia may not be associated with ECG changes.

If hyperkalemia is present, spironolactone and hydrochlorothiazide should be discontinued immediately. With severe hyperkalemia, the clinical situation dictates the procedures to be employed. These include the intravenous administration of calcium chloride solution, sodium bicarbonate solution and/or the oral or parenteral administration of glucose with a rapid-acting insulin preparation. These are temporary measures to be repeated as required. Cationic exchange resins such as sodium polystyrene sulfonate may be orally or rectally administered. Persistent hyperkalemia may require dialysis.

Hypokalemia may develop as a result of profound diuresis, particularly when spironolactone and hydrochlorothiazide is used concomitantly with loop diuretics, glucocorticoids, or ACTH, when severe cirrhosis is present or after prolonged therapy. Interference with adequate oral electrolyte intake will also contribute to hypokalemia. Hypokalemia may cause cardiac arrhythmias and may exaggerate the effects of digitalis therapy. Potassium depletion may induce signs of digitalis intoxication at previously tolerated dosage levels. Although any chloride deficit is generally mild and usually does not require specific treatment except under extraordinary circumstances (as in liver disease or renal disease), chloride replacement may be required in the treatment of metabolic alkalosis.

Spironolactone and hydrochlorothiazide therapy may cause a transient elevation of BUN. This appears to represent a concentration phenomenon rather than renal toxicity, since the BUN level returns to normal after use of spironolactone and hydrochlorothiazide is discontinued. Progressive elevation of BUN is suggestive of the presence of preexisting renal impairment.

Reversible hyperchloremic metabolic acidosis, usually in association with hyperkalemia, has been reported to occur in some patients with decompensated hepatic cirrhosis, even in the presence of normal renal function.

Dilutional hyponatremia, manifested by dryness of the mouth, thirst, lethargy, and drowsiness, and confirmed by a low serum sodium level, may be induced, especially when spironolactone and hydrochlorothiazide is administered in combination with other diuretics, and dilutional hyponatremia may occur in edematous patients in hot weather; appropriate therapy is water restriction rather than administration of sodium, except in rare instances when the hyponatremia is life-threatening. A true low-salt syndrome may rarely develop with spironolactone and hydrochlorothiazide therapy and may be manifested by increasing mental confusion similar to that observed with hepatic coma. This syndrome is differentiated from dilutional hyponatremia in that it does not occur with obvious fluid retention. Its treatment requires that diuretic therapy be discontinued and sodium administered.

Hyperuricemia may occur or acute gout may be precipitated in certain patients receiving thiazides. Thiazides have been shown to increase the urinary excretion of magnesium; this may result in hypomagnesemia. Increases in cholesterol and triglyceride levels may be associated with thiazide diuretic therapy.

In diabetic patients, dosage adjustments of insulin or oral hypoglycemic agents may be required. Hyperglycemia may occur with thiazide diuretics. Thus, latent diabetes mellitus may become manifest during thiazide therapy.

The antihypertensive effects of spironolactone and hydrochlorothiazide may be enhanced in the post-sympathetectomy patient. If progressive renal impairment becomes evident, consider withholding or discontinuing diuretic therapy.

Thiazides may decrease urinary calcium excretion. Thiazides may cause intermittent and slight elevation of serum calcium in the absence of known disorders of calcium metabolism. Marked hypercalcemia may be evidence of hidden hyperparathyroidism. Thiazides should be discontinued before carrying out tests for parathyroid function. Pathologic changes in the parathyroid gland with hypercalcemia and hypophosphatemia have been observed in patients on prolonged thiazide therapy.

Gynecomastia may develop in association with the use of spironolactone; physicians should be alert to its possible onset. The development of gynecomastia appears to be related to both dosage level and duration of therapy and is normally reversible when spironolactone and hydrochlorothiazide is discontinued. In rare instances some breast enlargement may persist when spironolactone and hydrochlorothiazide is discontinued.

Patients who receive spironolactone and hydrochlorothiazide should be advised to avoid potassium supplements and foods containing high levels of potassium including salt substitutes.

Periodic determination of serum electrolytes to detect possible electrolyte imbalance should be done at appropriate intervals, particularly in the elderly and those with significant renal or hepatic impairments.

Thiazides should be discontinued before carrying out tests for parathyroid function (see PRECAUTIONS: General). Thiazides may also decrease serum PBI levels without evidence of alteration of thyroid function.

Several reports of possible interference with digoxin radioimmunoassays by spironolactone or its metabolites have appeared in the literature. Neither the extent nor the potential clinical significance of its interference (which may be assay specific) has been fully established.

Canrenone, a major (and active) metabolite of spironolactone, appears in human breast milk. Because spironolactone has been found to be tumorigenic in rats, a decision should be made whether to discontinue the drug, taking into account the importance of the drug to the mother. If use of the drug is deemed essential, an alternative method of infant feeding should be instituted.

Safety and effectiveness in pediatrics patients have not been established.

The following adverse reactions have been reported and, within each category (body system), are uled in order of decreasing severity.

Body as a whole: Weakness.

Cardiovascular: Hypotension including orthostatic hypotension (may be aggravated by alcohol, barbiturates, narcotics or antihypertensive drugs).

Digestive: Pancreatitis, jaundice (intrahepatic cholestatic jaundice), diarrhea, vomiting, sialoadenitis, cramping, constipation, gastric irritation, nausea, anorexia.

Hematologic: Aplastic anemia, agranulocytosis, leukopenia, hemolytic anemia, thrombocytopenia.

Hypersensitivity: Anaphylactic reactions, necrotizing angitis (vasculitis and cutaneous vasculitis), respiratory distress including pneumonitis and pulmonary edema, photosensitivity, fever, urticaria, rash, purpura.

Metabolic: Electrolyte imbalance (see PRECAUTIONS), hyperglycemia, glycosuria, hyperuricemia.

Musculoskeletal: Muscle spasm.

Nervous System/Psychiatric: Vertigo, paresthesias, dizziness, headache, restlessness.

Renal: Renal failure, renal dysfunction, interstitial nephritis (see WARNINGS).

Skin: Erythema multiforme, pruritus.

Special Senses: Transient blurred vision, xanthopsia.

Digestive: Gastric bleeding, ulceration, gastritis, diarrhea and cramping, nausea, vomiting.

Endocrine: Gynecomastia (see PRECAUTIONS), inability to achieve or maintain erection, irregular menses or amenorrhea, postmenopausal bleeding. Carcinoma of the breast has been reported in patients taking spironolactone but a cause and effect relationship has not been established.

Hematologic: Agranulocytosis.

Hypersensitivity: Fever, urticaria, maculopapular or erythematous cutaneous eruptions, anaphylactic reactions, vasculitis.

Nervous System/Psychiatric: Mental confusion, ataxia, headache, drowsiness, lethargy.

Liver/Biliary: A very few cases of mixed cholestatic/hepatocellular toxicity, with one reported fatality, have been reported with spironolactone administration.

Renal: Renal dysfunction (including renal failure).

The oral LD₅₀ of spironolactone is greater than 1,000 mg/kg in mice, rats, and rabbits. The oral LD₅₀ of hydrochlorothiazide is greater than 10 g/kg in both mice and rats.

Acute overdosage of spironolactone may be manifested by drowsiness, mental confusion, maculopapular or erythematous rash, nausea, vomiting, dizziness, or diarrhea. Rarely, instances of hyponatremia, hyperkalemia (less commonly seen with spironolactone and hydrochlorothiazide because the hydrochlorothiazide component tends to produce hypokalemia), or hepatic coma may occur in patients with severe liver disease, but these are unlikely due to acute overdosage.

However, because this product contains both spironolactone and hydrochlorothiazide, the toxic effects may be intensified, and signs of thiazide overdosage may be present. These include electrolyte imbalance such as hypokalemia and/or hyponatremia. The potassium-sparing action of spironolactone may predominate and hyperkalemia may occur, especially in patients with impaired renal function. BUN determinations have been reported to rise transiently with hydrochlorothiazide. There may be CNS depression with lethargy or even coma.

Induce vomiting or evacuate the stomach by lavage. There is no specific antidote. Treatment is supportive to maintain hydration, electrolyte balance, and vital functions.

Patients who have renal impairment may develop spironolactone-induced hyperkalemia. In such cases, spironolactone and hydrochlorothiazide should be discontinued immediately. With severe hyperkalemia, the clinical situation dictates the procedures to be employed. These include the intravenous administration of calcium chloride solution, sodium bicarbonate solution and/or the oral or parenteral administration of glucose with a rapid-acting insulin preparation. These are temporary measures to be repeated as required. Cationic exchange resins such as sodium polystyrene sulfonate may be orally or rectally administered. Persistent hyperkalemia may require dialysis.

Optimal dosage should be established by individual titration of the components (see Box WARNING).

The usual maintenance dose of spironolactone and hydrochlorothiazide tablets is 100 mg each of spironolactone and hydrochlorothiazide daily, administered in a single dose or in divided doses, but may range from 25 mg to 200 mg of each component daily depending on the response to the initial titration. In some instances it may be desirable to administer separate tablets of either spironolactone or hydrochlorothiazide in addition to spironolactone and hydrochlorothiazide tablets in order to provide optimal individual therapy.

The onset of diuresis with spironolactone and hydrochlorothiazide occurs promptly and, due to prolonged effect of the spironolactone component, persists for two to three days after spironolactone and hydrochlorothiazide is discontinued.

Although the dosage will vary depending on the results of titration of the individual ingredients, many patients will be found to have an optimal response to 50 mg to 100 mg each of spironolactone and hydrochlorothiazide daily, given in a single dose or in divided doses.

Concurrent potassium supplementation is not recommended when spironolactone and hydrochlorothiazide is used in the long-term management of hypertension or in the treatment of most edematous conditions, since the spironolactone span of spironolactone and hydrochlorothiazide tablets is usually sufficient to minimize loss induced by the hydrochlorothiazide component.

Spironolactone and Hydrochlorothiazide Tablets are available containing 25 mg of spironolactone, USP and 25 mg of hydrochlorothiazide, USP.

The tablets are ivory, round, biconvex tablets debossed with M above the score and 41 below the score on one side of the tablet and blank on the other side. They are available as follows:

NDC 0378-0141-01
bottles of 100 tablets

NDC 0378-0141-05
bottles of 500 tablets