Biochemical and pharmacological consequences of the interaction between methotrexate and ketoprofen in the rabbit.

Severe methotrexate (MTX) toxicity is a proven complication of associations of MTX and non-steroidal anti-inflammatory drugs (NSAIDs). This study investigated the interaction between MTX (50 or 100 mg kg-1) and ketoprofen (KP) (3 mg kg-1 day-1, pretreatment for 8 days) in the rabbit. The drug association induced a reversible increase in blood urea and creatinine. The severity degree of renal dysfunction was significantly related to the MTX dose; it was not modified by prolonged exposure to KP after MTX administration. The biological markers of haematopoietic and hepatic functions were unchanged. Pretreatment by KP induced a marked reduction (70%) in the urinary excretion of the prostaglandin 6-keto-PGF1 alpha. MTX dose-related alterations in MTX pharmacokinetics were also observed with the drug association: at a MTX dose of 100 mg kg-1, the presence of KP significantly reduced the total body clearance, the renal clearance and the fraction of MTX eliminated in urine as compared to controls. An appreciable reduction in the plasma binding of MTX was also noted in vivo when KP was associated. This experimental study confirms the existence of an interaction between MTX and KP and demonstrates its renal origin.