Comparative bioavailability and pharmacokinetics of hydrochlorothiazide from oral tablet dosage forms, determined by plasma level and urinary excretion methods.

The bioavailability and pharmacokinetics of two hydrochlorothiazide products were compared following single 50 mg oral doses to 20 healthy male volunteers. Plasma and urine were assayed for hydrochlorothiazide by a specific and sensitive HPLC method. Plasma profiles of hydrochlorothiazide were adequately described by a triexponential function. The bioavailability of hydrochlorothiazide from the two brands did not differ significantly as judged by the values of Cmax, tmax, AUC0 leads to infinity, mean residence time, variance of residence time, and urinary excretion of unchanged drug. Close similarity was observed between urinary excretion rates and concentrations of drug in plasma.