Triamterene

INDICATIONS AND USAGE: 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 is indicated for the treatment of hypertension or edema in patients who develop hypokalemia on hydrochlorothiazide alone. Triamterene and hydrochlorothiazide is 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 may be used alone or in combination with other antihypertensive drugs, such as beta-blockers. Since triamterene and hydrochlorothiazide 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.

CLINICAL PHARMACOLOGY: Triamterene and hydrochlorothiazide tablets are diuretic, antihypertensive drug product, principally due to its hydrochlorothiazide component; the triamterene component of triamterene and hydrochlorothiazide tablets reduces the excessive potassium loss which may occur with hydrochlorothiazide use. Hydrochlorothiazide: Hydrochlorothiazide is a diuretic and antihypertensive agent. It blocks the renal tubular absorption of sodium and chloride ions. This natriuresis and diuresis is accompanied by a secondary loss of potassium and bicarbonate. Onset of hydrochlorothiazide’s diuretic effect occurs within 2 hours and the peak action takes place in 4 hours. Diuretic activity persists for approximately 6 to 12 hours. The exact mechanism of hydrochlorothiazide’s antihypertensive action is not known although it may relate to the excretion and redistribution of body sodium. Hydrochlorothiazide does not affect normal blood pressure. Following oral administration, peak hydrochlorothiazide plasma levels are attained in approximately 2 hours. It is excreted rapidly and unchanged in the urine. Well controlled studies have demonstrated that doses of hydrochlorothiazide as low as 25 mg given once daily are effective in treating hypertension, but the dose-response has not been clearly established. Triamterene: Triamterene is a potassium-conserving (antikaliuretic) diuretic with relatively weak natriuretic properties. It exerts its diuretic effect on the distal renal tubule to inhibit the reabsorption of sodium in exchange for potassium and hydrogen. With this action, triamterene increases sodium excretion and reduces the excessive loss of potassium and hydrogen associated with hydrochlorothiazide. Triamterene is not a competitive antagonist of the mineralocorticoids and its potassium-conserving effect is observed in patients with Addison’s disease, i.e., without aldosterone. Triamterene’s onset and duration of activity is similar to hydrochlorothiazide. No predictable antihypertensive effect has been demonstrated with triamterene. Triamterene is rapidly absorbed following oral administration. Peak plasma levels are achieved within one hour after dosing. Triamterene is primarily metabolized to the sulfate conjugate of hydroxytriamterene. Both the plasma and urine levels of this metabolite greatly exceed triamterene levels. The amount of triamterene added to 50 mg of hydrochlorothiazide in triamterene and hydrochlorothiazide 75mg/50mg tablets was determined from steady-state dose-response evaluations in which various doses of liquid preparations of triamterene were administered to hypertensive persons who developed hypokalemia with hydrochlorothiazide (50 mg given once daily). Single daily doses of 75 mg triamterene resulted in greater increases in serum potassium than lower doses (25 mg and 50 mg), while doses greater than 75 mg of triamterene resulted in no additional elevations in serum potassium levels. The amount of triamterene added to the

DOSAGE AND ADMINISTRATION: The usual dose of triamterene and hydrochlorothiazide tablets 37.5mg/25mg 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 75mg/ 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 triamterene and hydrochlorothiazide tablet 75mg/50mg daily or more than two triamterene and hydrochlorothiazide tablets 37.5mg/25mg daily. Clinical experience with the administration of two triamterene and hydrochlorothiazide tablets 37.5mg/25mg 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 75mg/50mg directly. Patients receiving 25 mg hydrochlorothiazide who become hypokalemic may be transferred to triamterene and hydrochlorothiazide tablets 37.5mg/25mg directly. In patients requiring hydrochlorothiazide therapy and in whom hypokalemia cannot be risked therapy may be initiated with triamterene and hydrochlorothiazide tablets 37.5mg/25mg. If an optimal blood pressure response is not obtained with triamterene and hydrochlorothiazide tablets 37.5mg/25mg, the dose should be increased to two triamterene and hydrochlorothiazide tablets 37.5mg/25mg daily as a single dose, or one triamterene and hydrochlorothiazide tablet 75mg/25mg 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 37.5mg/25mg daily. All patients changed from less bioavailable formulations to triamterene and hydrochlorothiazide tablets 75mg/50mg should be monitored clinically and for serum potassium after the transfer.

ADVERSE REACTIONS: Side effects observed in association with the use of triamterene and hydrochlorothiazide, 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.

WARNINGS: Hyperkalemia: Abnormal elevation of serum potassium levels (greater than or equal to 5.5 mEq/liter) can occur with all potassium-conserving diuretic combinations, including triamterene and hydrochlorothiazide. Hyperkalemia is more likely to occur in patients with renal impairment, diabetes (even without evidence of renal impairment), or elderly or severely ill patients. Since uncorrected hyperkalemia may be fatal, serum potassium levels must be monitored at frequent intervals especially in patients first receiving triamterene and hydrochlorothiazide, when dosages are changed or with any illness that may influence renal function. If hyperkalemia is suspected, (warning signs include paresthesias, muscular 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, triamterene and hydrochlorothiazide should be discontinued immediately and a thiazide alone should be substituted. If the serum potassium exceeds 6.5 mEq/liter, more vigorous therapy is required. 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. Cationic exchange resins such as sodium polystyrene sulfonate may be orally or rectally administered. Persistent hyperkalemia may require dialysis. The development of hyperkalemia associated with potassium-sparing diuretics is accentuated in the presence of renal impairment (see CONTRAINDICATIONS ). Patients with mild renal functional impairment should not receive this drug without frequent and continuing monitoring of serum electrolytes. Cumulative drug effects may be observed in patients with impaired renal function. The renal clearances of hydrochlorothiazide and the pharmacologically active metabolite of triamterene, the sulfate ester of hydroxytriamterene, have been shown to be reduced and the plasma levels increased following triamterene and hydrochlorothiazide administration to elderly patients and patients with impaired renal function. Hyperkalemia has been reported in diabetic patients with the use of potassium-conserving agents even in the absence of apparent renal impairment. Accordingly, triamterene and hydrochlorothiazide should be avoided in diabetic patients. If it is employed, serum electrolytes must be frequently monitored. Because of the potassium-sparing properties of angiotensin-converting enzyme (ACE) inhibitors, triamterene and hydrochlorothiazide should be used cautiously, if at all, with these agents (see PRECAUTIONS: Drug Interactions ). Metabolic or Respiratory Acidosis: Potassium-conserving therapy should also be avoided in severely ill patients in whom respiratory or metabolic acidosis may occur. Acidosis may be associated with rapid elevations in serum potassium levels. If triamterene and hydrochlorothiazide is employed, frequent evaluations of acid/base balance and serum electrolytes are necessary. Acute Myopia and Secondary Angle-Closure Glaucoma: Hydrochlorothiazide, a sulfonamide, can cause an idiosyncratic reaction, resulting in acute transient myopia and acute angle-closure glaucoma. Symptoms include acute onset of decreased visual acuity or ocular pain and typically occur within hours to weeks of drug initiation. Untreated acute angle-closure glaucoma can lead to permanent vision loss. The primary treatment is to discontinue hydrochlorothiazide as rapidly as possible. Prompt medical or surgical treatments may need to be considered if the intraocular pressure remains uncontrolled. Risk factors for developing acute angle-closure glaucoma may include a history of sulfonamide or penicillin allergy.

CONTRAINDICATIONS: 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.

OVERDOSAGE: No specific data are available regarding triamterene and hydrochlorothiazide overdosage in humans and no specific antidote is available. Fluid and electrolyte imbalances are the most important concern. Excessive doses of the triamterene component may elicit hyperkalemia, dehydration, nausea, vomiting and weakness and possibly hypotension. Overdosing with hydrochlorothiazide has been associated with hypokalemia, hypochloremia, hyponatremia, dehydration, lethargy (may progress to coma) and gastrointestinal irritation. Treatment is symptomatic and supportive. Therapy with triamterene and hydrochlorothiazide should be discontinued. Induce emesis or institute gastric lavage. Monitor serum electrolyte levels and fluid balance. Institute supportive measures as required to maintain hydration, electrolyte balance, respiratory, cardiovascular and renal function.