Hydrochlorothiazide (HCTZ) and triamterene are diuretics used together in an oral preparation to treat hypertension or edema. Hydrochlorothiazide is a thiazide diuretic, while triamterene is a potassium-sparing diuretic. In hypertension, diuretics are often used as initial therapy, either alone or in combination with other agents. Unlike the loop diuretics, the efficacy of this diuretic combination is diminished in patients with renal insufficiency. When marketed in 1965, Dyazide® was the first product to combine hydrochlorothiazide and triamterene. The original Dyazide® capsules, containing HCTZ 25 mg and TM 50 mg, had an oral bioavailability of approximately 50% compared to the reference standard suspension. Tablet formulations containing HCTZ 50 mg with TM 75 mg (i.e., Maxzide®), and HCTZ 25 mg with TM 37.5 mg (i.e., Maxzide®-25) were approved on 10/22/84 and 5/13/88, respectively. Maxzide® demonstrated improved bioavailability compared to the original Dyazide® product. On 3/3/94, Dyazide® capsules were reformulated. The current formulation of Dyazide® capsules (HCTZ 25 mg with TM 37.5 mg), has an improved relative bioavailability that is comparable to the reference standard suspension. Bioavailability data comparing Maxzide®-25 mg with the current Dyazide® formulation are not available.