Common Drug Interactions with Methotrexate
Methotrexate, used for rheumatoid arthritis, psoriasis, and cancer, interacts with many medications by affecting its clearance, toxicity, or efficacy. It is primarily cleared by the kidneys and competes with other drugs for renal secretion or protein binding. Key interactions include NSAIDs (e.g., ibuprofen, naproxen), which reduce methotrexate excretion and raise toxicity risk, leading to severe side effects like bone marrow suppression and acute kidney injury.[1]
Proton pump inhibitors (PPIs) such as omeprazole and pantoprazole inhibit methotrexate transport, causing prolonged exposure and elevated levels, as seen in case reports of profound cytopenias.[1][2]
Antibiotics That Increase Methotrexate Levels
Penicillins (e.g., amoxicillin) and sulfonamides (e.g., sulfamethoxazole in Bactrim) displace methotrexate from plasma proteins and block tubular secretion, potentially causing fatal myelosuppression. Guidelines recommend monitoring levels and holding methotrexate during such courses.[1][3]
Trimethoprim (often with sulfamethoxazole) mimics folate antagonism, amplifying bone marrow toxicity.[2]
Interactions with Pain Relievers and Anti-Inflammatories
Aspirin and high-dose salicylates compete for renal excretion, increasing methotrexate concentrations. Low-dose aspirin (for cardioprotection) has lower risk but still warrants caution and monitoring.[1]
Cyclosporine drastically raises methotrexate exposure (up to 3-5 fold), heightening nephrotoxicity; combination is generally avoided.[3]
Antipsychotics, Antidiabetics, and Other Common Meds
Chloramphenicol, ciprofloxacin, and probenecid inhibit methotrexate elimination, risking accumulation.[1]
Leflunomide (another DMARD) adds hepatotoxicity when combined; sequential use requires washout.[3]
Theophylline clearance slows with methotrexate, requiring dose adjustments.[2]
How These Interactions Happen and Monitoring
Most occur via reduced renal clearance (OAT transporters), protein displacement, or additive folate inhibition. High-dose methotrexate (cancer regimens) poses greater risks than low-dose (autoimmune).[1]
Monitor CBC, liver enzymes, creatinine, and methotrexate levels (if high-dose). Hold interacting drugs 2-3 days before/after methotrexate; rescue with leucovorin for toxicity.[3]
Foods, Alcohol, and OTCs to Avoid
Alcohol worsens hepatotoxicity. Avoid high-dose folic acid supplements (interfere with efficacy) but use low-dose (1mg) as recommended.[2]
Herbals like echinacea may induce liver enzymes, altering levels unpredictably.[1]
When to Consult a Doctor
Any new med, OTC, or supplement requires review. Rheumatologists often use interaction checkers or pharmacy consults. Dialysis patients face heightened risks due to erratic clearance.[3]
Sources
[1] Drugs.com - Methotrexate Interactions
[2] Medscape - Methotrexate Drug Interactions
[3] UpToDate - Methotrexate Drug Interactions