TRIAMTERENE AND HYDROCHLOROTHIAZIDE

Triamterene and hydrochlorothiazide combines triamterene a potassium-conserving diuretic, with the natriuretic agent, hydrochlorothiazide. Each Triamterene and Hydrochlorothiazide Tablet USP, 37.5 mg/25 mg contains: Triamterene, USP ..............................................................................37.5 mg Hydrochlorothiazide, USP ................................................................25 mg Each Triamterene and Hydrochlorothiazide Tablet USP, 75 mg/50 mg contains: Triamterene, USP .............................................................................75 mg Hydrochlorothiazide, USP ................................................................50 mg Each triamterene and hydrochlorothiazide tablet, USP intended for oral administration contains 37.5 mg triamterene USP with 25 mg hydrochlorothiazide USP and 75 mg triamterene USP with 50 mg hydrochlorothiazide USP. In addition, each tablet contains the following inactive ingredients: colloidal silicon dioxide, croscarmellose sodium, D&C Yellow No. 10 Aluminum Lake, hypromellose, magnesium stearate and microcrystalline cellulose. Additionally, the 37.5 mg/25 mg tablets contain FD&C Blue No. 1 Aluminum Lake. Triamterene is 2,4,7-triamino-6-phenylpteridine. Triamterene, USP is soluble in formic acid. It is sparingly soluble in methoxyethanol. It is very slightly soluble in acetic acid, alcohol and dilute mineral acids. It is practically insoluble in water, benzene, ether, chloroform and dilute alkali hydroxides. Its molecular weight is 253.26. Its structural formula is: Hydrochlorothiazide is 6-chloro-3,4-dihydro-2 H -1,2,4, benzothiadiazine-7-sulfonamide 1,1-dioxide. Hydrochlorothiazide, USP is very slightly soluble in water. It is freely soluble in sodium hydroxide solution, n-butylamine and dimethyl formamide. It is sparingly soluble in methanol. It is insoluble in ether, chloroform and dilute mineral acids. Its molecular weight is 297.7. Its structural formula is: figure figure

This fixed combination drug is not indicated for the initial therapy of edema or hypertension except in individuals in whom the development of hypokalemia cannot be risked. Triamterene and hydrochlorothiazide tablets, USP are indicated for the treatment of hypertension or edema in patients who develop hypokalemia on hydrochlorothiazide alone. Triamterene and hydrochlorothiazide tablets, USP are also indicated for those patients who require a thiazide diuretic and in whom the development of hypokalemia cannot be risked (e.g., patients on concomitant digitalis preparations, or with a history of cardiac arrhythmias, etc.). Triamterene and hydrochlorothiazide tablets, USP may be used alone or in combination with other antihypertensive drugs, such as beta-blockers. Since triamterene and hydrochlorothiazide tablets, USP may enhance the actions of these drugs, dosage adjustments may be necessary. 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 pathological causes or from the physiologic and mechanical consequences of pregnancy. Thiazides are indicated in pregnancy when edema is due to pathologic causes, just as they are in the absence of pregnancy. 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 which is harmful to neither the fetus nor the mother (in the absence of cardiovascular disease), but which 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 which is not relieved by rest. In these cases, a short course of diuretics may provide relief and may be appropriate.

The usual dose of triamterene and hydrochlorothiazide tablets, 37.5 mg/25 mg is one or two tablets daily, given as a single dose, with appropriate monitoring of serum potassium ( see WARNINGS ). The usual dose of triamterene and hydrochlorothiazide tablets, 75 mg/50 mg is one tablet daily, with appropriate monitoring of serum potassium ( see WARNINGS ). There is no experience with the use of more than one 75 mg/50 mg (75 mg triamterene and 50 mg hydrochlorothiazide) tablet daily or more than two 37.5 mg/25 mg (37.5 mg triamterene and 25 mg hydrochlorothiazide) tablets daily. Clinical experience with the administration of two 37.5 mg/25 mg (37.5 mg triamterene and 25 mg hydrochlorothiazide) tablets daily in divided doses (rather than as a single dose) suggests an increased risk of electrolyte imbalance and renal dysfunction. Patients receiving 50 mg of hydrochlorothiazide who become hypokalemic may be transferred to triamterene and hydrochlorothiazide tablets, 75 mg/50 mg directly. Patients receiving 25 mg hydrochlorothiazide who become hypokalemic may be transferred to triamterene and hydrochlorothiazide tablets, 37.5 mg/25 mg directly. In patients requiring hydrochlorothiazide therapy and in whom hypokalemia cannot be risked therapy may be initiated with triamterene and hydrochlorothiazide tablets, 37.5 mg/25 mg. If an optimal blood pressure response is not obtained with triamterene and hydrochlorothiazide tablets, 37.5 mg/25 mg, the dose should be increased to two 37.5 mg/25 mg (37.5 mg triamterene and 25 mg hydrochlorothiazide) tablets daily as a single dose, or one triamterene and hydrochlorothiazide tablets, 75 mg/50 mg daily. If blood pressure still is not controlled, another antihypertensive agent may be added ( see PRECAUTIONS: Drug Interactions ). Clinical studies have shown that patients taking less bioavailable formulations of triamterene and hydrochlorothiazide in daily doses of 25 mg to 50 mg hydrochlorothiazide and 50 mg to 100 mg triamterene may be safely changed to one triamterene and hydrochlorothiazide tablets, 37.5 mg/25 mg daily. All patients changed from less bioavailable formulations to triamterene and hydrochlorothiazide tablets, 75 mg/50 mg should be monitored clinically and for serum potassium after the transfer.

Hyperkalemia Triamterene and hydrochlorothiazide should not be used in the presence of elevated serum potassium levels (greater than or equal to 5.5 mEq/liter). If hyperkalemia develops, this drug should be discontinued and a thiazide alone should be substituted. Antikaliuretic Therapy or Potassium Supplementation Triamterene and hydrochlorothiazide should not be given to patients receiving other potassium-conserving agents such as spironolactone, amiloride hydrochloride or other formulations containing triamterene. Concomitant potassium supplementation in the form of medication, potassium-containing salt substitute or potassium-enriched diets should also not be used. Impaired Renal Function Triamterene and hydrochlorothiazide is contraindicated in patients with anuria, acute and chronic renal insufficiency or significant renal impairment. Hypersensitivity Triamterene and hydrochlorothiazide should not be used in patients who are hypersensitive to triamterene or hydrochlorothiazide or other sulfonamide-derived drugs.

Side effects observed in association with the use of triamterene and hydrochlorothiazide tablets, other combination products containing triamterene/hydrochlorothiazide, and products containing triamterene or hydrochlorothiazide include the following: Gastrointestinal: jaundice (intrahepatic cholestatic jaundice), pancreatitis, nausea, appetite disturbance, taste alteration, vomiting, diarrhea, constipation, anorexia, gastric irritation, cramping. Central Nervous System: drowsiness and fatigue, insomnia, headache, dizziness, dry mouth, depression, anxiety, vertigo, restlessness, paresthesias. Cardiovascular: tachycardia, shortness of breath and chest pain, orthostatic hypotension (may be aggravated by alcohol, barbiturates or narcotics). Renal: acute renal failure, acute interstitial nephritis, renal stones composed of triamterene in association with other calculus materials, urine discoloration. Hematologic: leukopenia, agranulocytosis, thrombocytopenia, aplastic anemia, hemolytic anemia and megaloblastosis. Ophthalmic: xanthopsia, transient blurred vision. Hypersensitivity: anaphylaxis, photosensitivity, rash, urticaria, purpura, necrotizing angiitis (vasculitis, cutaneous vasculitis), fever, respiratory distress including pneumonitis. Other: muscle cramps and weakness, decreased sexual performance and sialadenitis. Whenever adverse reactions are moderate to severe, therapy should be reduced or withdrawn. Altered Laboratory Findings Serum Electrolytes: hyperkalemia, hypokalemia, hyponatremia, hypomagnesemia, hypochloremia ( see WARNINGS and PRECAUTIONS ). Creatinine , Blood Urea Nitrogen: Reversible elevations in BUN and serum creatinine have been observed in hypertensive patients treated with triamterene and hydrochlorothiazide. Glucose: hyperglycemia, glycosuria and diabetes mellitus ( see PRECAUTIONS ). Serum Uric Acid , PBI and Calcium: ( see PRECAUTIONS ). Other: Elevated liver enzymes have been reported in patients receiving triamterene and hydrochlorothiazide. Postmarketing Experience Non-melanoma Skin Cancer: Hydrochlorothiazide is associated with an increased risk of non-melanoma skin cancer. In a study conducted in the Sentinel System, increased risk was predominantly for squamous cell carcinoma (SCC) and in white patients taking large cumulative doses. The increased risk for SCC in the overall population was approximately 1 additional case per 16,000 patients per year, and for white patients taking a cumulative dose of ≥ 50,000 mg the risk increase was approximately 1 additional SCC case for every 6,700 patients per year.

Thiazides may add to or potentiate the action of other antihypertensive drugs. The thiazides may decrease arterial responsiveness to norepinephrine. This diminution is not sufficient to preclude effectiveness of the pressor agent for therapeutic use. Thiazides have also been shown to increase the responsiveness to tubocurarine. Lithium generally should not be given with diuretics because they reduce its renal clearance and add a high risk of lithium toxicity. Refer to the package insert on lithium before use of such concomitant therapy. Acute renal failure has been reported in a few patients receiving indomethacin and formulations containing triamterene and hydrochlorothiazide. Caution is therefore advised when administering non-steroidal anti-inflammatory agents with triamterene and hydrochlorothiazide. Potassium-sparing agents should be used very cautiously, if at all, in conjunction with angiotensin-converting enzyme (ACE) inhibitors due to a greatly increased risk of hyperkalemia. Serum potassium should be monitored frequently.