Pterin Drug Interactions

Concomitant administration with the following drugs decrease methotrexate-transport function which results in the delay of elimination and action of methotrexate or enhancement of its toxicity: Nonsteroidal anti-inflammatory agents like salicylates, sulfonamides, tetracycline, chloramphenicol, phenytoin, barbiturates, aminobenzoate, propionic acid, anti-inflammatory agents, probenecid and sulfinpyrazone.
This drug has wide protein-bound ability and it can be substituted by acidic agents like salicylate, phenylbutazone, phenytoin and sulfonamides. Therefore, the toxicity can be increased.
Rarely, the complex drug of sulfamethoxazole and trimethoprim can increase its action. Concomitant administration with complex drug of sulfamethoxazole and trimethoprim may increase the concentration of methotrexate.
Concomitant intraspinal administration of this drug with radiotherapeutics to central nervous system should not be recommended because it has reportedly caused leukoencephalopathy.