Label: TRIAMTERENE AND HYDROCHLOROTHIAZIDE tablet

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 25 mg of hydrochlorothiazide in triamterene and hydrochlorothiazide 37.5mg/25mg tablets was also 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 (25 mg given once daily). Single daily doses of 37.5 mg triamterene resulted in greater increases in serum potassium than a lower dose (25 mg), while doses greater than 37.5 mg of triamterene, i.e., 75 mg and 100 mg, resulted in no additional elevations in serum potassium levels. The dose-response relationship of triamterene was also evaluated in patients rendered hypokalemic by hydrochlorothiazide given 25 mg twice daily. Triamterene given twice daily increased serum potassium levels in a dose related fashion. However, the combination of triamterene and hydrochlorothiazide given twice daily also appeared to produce an increased frequency of elevation in serum BUN and creatinine levels. The largest increases in serum potassium, BUN and creatinine in this study were observed with 50 mg of triamterene given twice daily, the largest dose tested. Ordinarily, triamterene does not entirely compensate for the kaliuretic effect of hydrochlorothiazide and some patients may remain hypokalemic while receiving triamterene and hydrochlorothiazide. In some individuals, however, it may induce hyperkalemia (see WARNINGS).

The triamterene and hydrochlorothiazide components of triamterene and hydrochlorothiazide 75mg/50mg tablets and triamterene and hydrochlorothiazide 37.5mg/25mg tablets are well absorbed and are bioequivalent to liquid preparations of the individual components administered orally. Food does not influence the absorption of triamterene or hydrochlorothiazide from triamterene and hydrochlorothiazide 75mg/50mg tablets or triamterene and hydrochlorothiazide 37.5mg/25mg tablets. The hydrochlorothiazide component of triamterene and hydrochlorothiazide 75mg/50mg tablets is bioequivalent to single entity hydrochlorothiazide tablet formulations.

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.

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.

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.

Metabolic and Endocrine Effects:The thiazides may decrease serum PBI levels without signs of thyroid disturbance.

Calcium excretion is decreased by thiazides. Pathological changes in the parathyroid gland with hypercalcemia and hypophosphatemia have been observed in a few patients on prolonged thiazide therapy. The common complications of hyperparathyroidism such as renal lithiasis, bone resorption, and peptic ulceration have not been seen. Thiazides should be discontinued before carrying out tests for parathyroid function.

Insulin requirements in diabetic patients may be increased, decreased or unchanged. Diabetes mellitus which has been latent may become manifest during thiazide administration.

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

Possible exacerbation or activation of systemic lupus erythematosus by thiazides has been reported.

Drug Interactions: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.

Drug/Laboratory Test Interactions:Triamterene and quinidine have similar fluorescence spectra; thus triamterene and hydrochlorothiazide may interfere with the measurement of quinidine.

Nursing Mothers:Thiazides and triamterene in combination have not been studied in nursing mothers. Triamterene appears in animal milk and this may occur in humans. Thiazides are excreted in human breast milk. If use of the combination drug product is deemed essential, the patient should stop nursing.

Pediatric Use:Safety and effectiveness in pediatric patients have not been established.

Information for Patients: Non-melanoma Skin Cancer:Instruct patients taking hydrochlorothiazide to protect skin from the sun and undergo regular skin cancer screening.