Abstract

The concurrent use of herbal drugs and orthodox medicines for the treatment of various health

conditions is a common practice amongst patients; a practice that could result in drug-herb

interaction. This study evaluates the effects of Hibiscus sabdariffawater extract on thein vitro

and in vivo availability, as well as pharmacokinetics of metforminand lisinopril in healthy

human volunteers.For the determination of metformin and lisinopril in vitroin simulated

physiological pHs(0.1 M HCl, phosphate buffers pH of 6.8 and 7.4), three simples UV

spectrophotometric methodswere developed and validated according to ICH guidelines. The

in vitroavailability of metformin and lisinopril alone and in presence of Hibiscus sabdariffa

calyxes water extracts (1 g/L) in each of the three media(1 L and 900 mL) were

determinedusing dissolution apparatus (BP, 2013) set at 100and 50 rpm at 37 °C. Samples (5

mL) withdrawn from the media at 5, 10, 15, 30, 45, and 60 min were analysed for the

metformin and lisinopril content released using the appropriate developed method. For the

quantification of metformin and lisinopril in the in vivostudy, a RP-HPLC method was

developed and validated for each drug using caffeine as internal standard IS.The optimized

conditions comprise of a Chemsl ODS®C18 column (200 x 4.6 mm), binary mobile phase

(Methanol: Water 80:20)containing 0.1 % orthophosphoric acid as additive, isocratic elution

mode, 232 and 218 nm detection wavelengths flow rate of 1.0 mL/min and 10 µL injection