Major
Acetylsalicylic acid × Methotrexate
Antiplatelet agents (low dose) / NSAIDs (analgesic dose)×Antimetabolites, folic acid analogues
Mechanism
Aspirin suppresses tubular secretion of methotrexate and displaces it from albumin binding. Methotrexate plasma levels rise – particularly dangerous at oncologic doses.
Symptoms
Mouth ulcers (mucositis), nausea, diarrhoea, hair loss. Blood counts fall: leukocytes, platelets, erythrocytes. Severe cases include fatal pancytopenia, nephrotoxicity, and hepatotoxicity.
Management
At oncologic methotrexate doses, the combination is not prescribed. At low rheumatologic doses (5–25 mg/week), cardioprotective aspirin (75–100 mg/day) is acceptable when renal function is preserved, with full blood count and creatinine every 1–3 months.