Effect of silymarin on the oral bioavailability of ranitidine in healthy human volunteers

The effect of silymarin pretreatment on the pharmacokinetics of ranitidine was investigated in 12 healthy male human volunteers aged 19-26 years. After an overnight fast, ranitidine 150 mg was administered to the volunteers either alone or after 7 days pretreatment with thrice daily dose of 140 mg silymarin. The wash-out period between each treatment was 7 days. Serum levels of ranitidine were determined by HPLC. Pharmacokinetic parameters were determined based on non-compartmental model analysis using the computer program KINETICA. There was no influence of silymarin on the pharmacokinetics of ranitidine. Concomitant administration of silymarin at this dosage did not alter ranitidine C(max) and AUC(0-infinity). There was a significant difference in area under the first moment curve (AUMC) and mean residence time. This result is useful in predicting the interaction of silymarin with other cytochrome 3A4 and P-glycoprotein substrates at normal dosage.