Influence of co-trimoxazole on methotrexate pharmacokinetics in children with acute lymphoblastic leukemia.

The effect of co-trimoxazole on methotrexate (MTX) pharmacokinetics was studied in seven children with ALL in remission receiving weekly maintenance therapy. Each child received MTX alone during one course, and MTX with co-trimoxazole during the next. Co-trimoxazole did not cause any significant alteration in either intestinal absorption of MTX, the degree of MTX plasma protein binding, or the average concentration X time exposure to MTX. These results indicate that low doses of co-trimoxazole do not perturb the serum pharmacokinetics of MTX. However, interaction of these drugs at the cellular level still remains a distinct possibility.