Absorption and disposition of a new low-dose combination formulation of hydrochlorothiazide and triamterene.

Two studies are reported that assess the bioequivalence of a new half-strength drug combination containing 25 mg hydrochlorothiazide and 37.5 mg triamterene compared to a full-strength formulation containing 50 mg hydrochlorothiazide and 75 mg triamterene. The first study (I) compared the absorption and disposition of the two drugs after administration of two tablets of the half-strength product as a single dose compared to a single dose of the full-strength product. The second study (II) assessed the bioavailability of the new product given as a single tablet on two occasions separated by an interval of 12 h compared to the full-strength product given as a single dose. Urine parameters in the first study indicated bioequivalence of the half-strength to the full product for both rate and extent of absorption. When given in divided doses, the half-strength product demonstrated bioequivalence to the full-strength product for extent of absorption. Additional data from the second study suggest that absorption of triamterene is greater when given in smaller divided doses and when given at night.