Drug interaction between celecoxib and methotrexate in organic anion transporter 3–transfected renal cells and in rats in vivo

Methotrexate has a clinically important pharmacokinetic interaction with nonsteroidal anti-inflammatory drugs (NSAIDs) mainly through its competition for tubular secretion via the renal organic anion transporter 3 (OAT3). We have previously reported the usefulness of OAT3-transfected renal tubular cells for screening of the drugs which interfere with the pharmacokinetics of methotrexate. Celecoxib, a cyclooxygenase (COX) 2 inhibitor, has not been reported to interact with methotrexate, but the mechanisms are unclear why the interaction did not occur. The purpose of this study was to evaluate the effect of celecoxib on methotrexate tubular secretion using a renal cell line stably expressing human OAT3 (S2-hOAT3), and to evaluate the pharmacokinetic interaction of the two drugs in rats. [3H]methotrexate uptake into S2-hOAT3 cells was significantly inhibited by celecoxib in a concentration-dependent manner and the Ki value was 35.3 µM. However, methotrexate serum concentrations and urinary excretion of methotrexate over 24 h in rats were not affected by celecoxib (50, 200 mg/kg). Celecoxib serum concentrations were increased by the increase in celecoxib dosage and the maximum drug concentration (Cmax) was 20.6 µM (celecoxib 200 mg/kg), which did not reach the Ki value obtained in the in vitro study. These results indicated that celecoxib inhibited the secretion of methotrexate via hOAT3, which suggested that celecoxib was a substrate of hOAT3. However, co-administration of the two drugs at clinical dosage did not affect the pharmacokinetics of methotrexate, because the serum concentrations did not reach the Ki value. Although the accumulation study using S2-hOAT3 cells was useful to predict the interaction between the new drug and methotrexate in vivo, a comparison of the Ki value with the Cmax in clinical dosage was necessary to evaluate the degree of this interaction.