Efficacy of Urine Samples in Biioavailability Study of Ranitidine

Urinary excretion of ranitidine is known to be almost 70% of the intact drug , therefore this drug would be a good candidate for bioavailability studies using urine samples. In this study the bioequivalency of two marketed formulations using both urine and plasma samples were investigated. 'Ranitidine' 150 mg tablets (generic) and 'Zantac' 150 mg tablets were compared in a double blind crossover study using eight healthy male volunteers. A simple and rapid HPLC method was also developed to analyze the drug concentration in both urine and plasma. Double peak phenomenon, observed in plasma samples, was omitted when the urine samples were used. Bioavailability of the two formulations calculated from urinary data were not significantly different, whereas the plasma data were considerably different (based on Cmax & Tmax but not AUC). Pharmacokinetic parameters resulted from urine regarding the rate of the absorption (Tmax-ud, (dDu/dt)max, Ka-ud) did not correlate well with their respective plasma parameters (Tmax, Cmax, Ka), whereas those of absorption extent and elimination rates (plasma AUC, K and urinary Du ) were well correlated. It is concluded that the urine sampling which has advantages of easy sample collection and extraction could be used for determination of the extent of absorption and rate of the elimination of ranitidine, since similar parameters can be obtained with easier sample collection and extraction, whereas for determination of absorption rate, Cmax & Tmax plasma data are preferred. Key words: Ranitidine, Bioavailability, HPLC, Plasma, Urine.