The renal drug-drug interaction between famotidine (an H(2) receptor antagonist) and probenecid has not been reproduced in rats. We have proposed that this is caused by a species difference in the transport activity by human/rat organic anion transporter (OAT) 3 and the expression of organic cation transporter (OCT) 1 in the rodent kidney. Since monkey OATs (mkOATs) exhibit similar transport activities to human orthologs, it is hypothesized that in vivo studies in monkeys will allow a more precise prediction of renal drug-drug interactions in humans. Famotidine and cimetidine were efficiently taken up by mkOAT3-expressing human embryonic kidney cells (Km, 154 and 71 microM, respectively), and their uptake was strongly inhibited by probenecid (Ki, 3.0-5.7 microM). Quantification of mkOCT1 and mkOCT2 mRNAs in the monkey kidney using real-time reverse transcription-polymerase chain reaction revealed their predominant expression in the liver and kidney, respectively. Crossover studies were conducted in cynomolgus monkeys. Famotidine was given by i.v. administration, with or without probenecid. Probenecid treatment caused a 65% reduction in the renal clearance (0.426 +/- 0.079 versus 0.165 +/- 0.027 l/h/kg) and a 90% reduction in the tubular secretion clearance (0.275 +/- 0.075 versus 0.0230 +/- 0.0217 l/h/kg), whereas it had no effect on the renal clearance of cimetidine. In contrast to the species-dependent effect of probenecid, allometric scaling using animal data (rat, dog, and monkey) successfully predicted the renal and tubular secretion clearance of famotidine in humans. These results suggest that monkeys are more appropriate animal species for predicting the renal drug-drug interactions in humans.