Penicillins:
Comment:
In patients receiving antineoplastic doses of methotrexate penicillins such as amoxicillin, carbenicillin, mezlocillin, oxacillin, and piperacillin have been associated with methotrexate toxicity such as bone marrow suppression and GI toxicity. A causal relationship is not well established, but the severity of the reactions dictates caution. The effect of other penicillins is not established, but one should be alert for evidence of methotrexate toxicity if any penicillin is given (especially if large doses are used). The risk with low-dose methotrexate (e.g., for arthritis) is probably much lower, but one should still be alert for evidence of methotrexate toxicity. Pralatrexate concentrations are increased by probenecid; caution with other inhibitors of renal clearance such as penicillins is warranted.
Class 2: Use Only if Benefit Felt to Outweigh Risk