[Pharmacological effects of phase-I- and phase-II-metabolites of triamterene (author's transl)].

Since triamterene (TA) is rapidly metabolized to hydroxytriamterene (OH-TA) and then to its sulfuric acid ester (OH-TA-ester) the question arose whether the metabolites are still effective on ion transport as is triamterene. The effect of the metabolites was studied in microperfusion experiments on the rat submaxillary duct, which resembles the distal nephron and is considered the site of action of triamterene. Added to the lumen the phase-I- as well as the phase-II-metabolites decreased reabsorption of Na+, secretion of K+, and yielded an accumulation of HCO3-. These effects of the metabolites were produced by equimolar concentrations and are almost identical to those of native triamterene. In conclusion, the phase-II-metabolite must be considered to be essentially responsible for the natriuresis and antikaliuresis observed after oral administration of triamterene.