Abstract: The effect of cimetidine on the elimination of praziquantel (PQT) in rats was studied. The results showed that cimetidine 100 mg/kg, ip 2 reduced the clearances of intravenous and oral PQT by 60 and 69 percent respectively. Cimetidine also markedly reduced liver blood flow of rats (a reduction of 58%) and inhibited PQT metabolism in hepatic microsomes of rats (an inhibition of 55%). The reduction in clearance of intravenous PQT could be attributed to the result of cimetidine lowering liver blood flow, whereas the reduction in clearance of oral PQT might be related mainly to the inhibition of cimetidine on the activity of hepatic drug-metabolizing enzymes.

Key words: Praziquantel, Cimetidine, Drug interaction, Drug metabolism