Bioavailability study of triamterene and xipamide using urinary pharmacokinetic data following single oral dose of each drug or their combination.

An efficient chromatographic method for the simultaneous determination of triamterene (TRI) and xipamide (XIP) in urine samples, based on high performance liquid chromatography with photodiode array detector (HPLC-DAD) has been developed. The HPLC separation was performed on a RP stainless-steel C-18 analytical column (250 mm × 4.6 mm, 5 μm) with a gradient elution system of 0.05 M phosphate buffer adjusted to pH 4.0 and methanol as the mobile phase. The method was used to determine the urinary excretion profile and to calculate different urinary pharmacokinetic parameters following oral dose of their combination compared with single oral doses of each drug and hence comparing their bioavailability. Quantitation was performed using chlorthalidone as internal standard. The calibration graphs of each drug were rectilinear in the range of 0.2-40 μg/mL urine for TRI and 0.2-15 μg/mL urine for XIP. An HPLC-DAD method was also successfully developed for the simultaneous determination of the investigated drugs in pharmaceutical preparations. The methods were validated in terms of linearity, accuracy, precision, selectivity, limits of detection and quantitation and other aspects of analytical validation.