Which medications should be avoided when taking methotrexate?

Medications to Avoid with Methotrexate

Several medications should be avoided or used with extreme caution when taking methotrexate, with trimethoprim-sulfamethoxazole (co-trimoxazole) being the most dangerous combination that should be strictly avoided, while NSAIDs require careful risk assessment and monitoring. 1, 2

Absolute Contraindications

Trimethoprim-Sulfamethoxazole (Co-trimoxazole)

• Co-trimoxazole, trimethoprim, and other antifolate drugs should be avoided in patients taking methotrexate due to severe risk of bone marrow suppression and life-threatening pancytopenia 1, 3
• This combination has resulted in fatal toxicity in multiple case reports, with severe pancytopenia occurring even at low doses of methotrexate 3
• The mechanism involves additive folic acid deficiency, leading to profound immunosuppression and cytopenia, particularly in elderly patients with renal impairment 1, 4
• If antibiotics are required for severe infection, methotrexate should be stopped until the patient recovers and the antibiotic course is complete 1

Medications Requiring Extreme Caution

Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

• NSAIDs should NOT be administered prior to or concomitantly with high-dose methotrexate (such as used in cancer treatment) due to risk of fatal toxicity 2
• For low-dose methotrexate (≤15 mg/week for rheumatoid arthritis or psoriasis), NSAIDs can be used with appropriate precautions in patients with normal renal function, but this carries increased risk 5, 2
• A 2018 Danish cohort study demonstrated that concomitant use of low-dose methotrexate and NSAIDs increased the risk of serious adverse events by 40% (weighted hazard ratio 1.40; 95% CI, 1.07-1.82), with significantly increased risk of acute renal failure and cytopenia 6
• NSAIDs reduce renal elimination of methotrexate by decreasing tubular secretion, leading to elevated and prolonged serum methotrexate levels 1, 2
• Specific NSAIDs with documented toxicity include naproxen, diclofenac, ibuprofen, and indomethacin 1, 5

Monitoring requirements when NSAIDs must be used with low-dose methotrexate:

• Baseline complete blood count with differential, liver function tests (ALT, AST), and renal function tests (BUN, creatinine) 5
• More frequent monitoring of renal function tests, especially in elderly patients or those with pre-existing renal impairment 5
• More frequent monitoring of liver function tests 5
• Withhold or decrease methotrexate if total white blood cell count <3 × 10⁹/L, neutrophils <1.0 × 10⁹/L, platelets <100,000/L, or liver enzymes ≥3 × upper limit of normal for 2 consecutive months 5

Other Hepatotoxic Agents

• Methotrexate should be used with caution when combined with other hepatotoxic drugs including alcohol, azathioprine, retinoids, and sulfasalazine 1, 2
• Patients receiving concomitant hepatotoxic agents should be closely monitored for possible increased risk of hepatotoxicity 2

Medications That Increase Methotrexate Toxicity

Drugs Affecting Renal Elimination

• Probenecid reduces renal tubular transport of methotrexate and should be used with careful monitoring 2, 7
• Penicillins may reduce renal clearance of methotrexate, with increased serum concentrations and concomitant hematologic and gastrointestinal toxicity reported 2
• Ciclosporin reduces renal elimination 1

Drugs Affecting Protein Binding

• Salicylates (including high-dose aspirin), phenylbutazone, phenytoin, and sulfonamides displace methotrexate from serum albumin, potentially increasing toxicity 2, 1
• High-dose aspirin has been associated with mild abnormalities of liver enzymes 4

Antibiotics

• Tetracyclines, chloramphenicol, and ciprofloxacin have been shown to increase methotrexate levels when high-dose methotrexate is used, though this does not appear to be an issue with low-dose therapy 1
• These antibiotics may decrease intestinal absorption or interfere with enterohepatic circulation 2
• Patients on long-term antibiotics (such as for acne) may require more frequent monitoring 1

Special Populations at Higher Risk

• Elderly patients are at particularly high risk for drug interactions due to diminished hepatic and renal function and decreased folate stores; relatively low doses should be considered with close monitoring 2
• Patients with renal impairment have significantly increased risk of toxicity with all interacting medications, particularly NSAIDs and trimethoprim 1, 5
• Patients taking nephrotoxic medications (ACE inhibitors, diuretics) should avoid or use extreme caution with NSAIDs and methotrexate 5

Critical Monitoring Parameters

• Baseline assessment should include complete blood count with differential and platelet counts, hepatic enzymes, renal function tests, and chest X-ray 2
• During therapy, hematology monitoring at least monthly, with renal and liver function every 1-2 months 2
• More frequent monitoring during periods of increased risk of elevated methotrexate blood levels (dehydration, new medications) 2

Patient Education Essentials

• Patients must report immediately any unusual bruising or bleeding, severe sore throat, mouth ulceration, dark urine, shortness of breath, or fever 1, 5
• Patients should inform all healthcare providers about methotrexate use before starting any new medications 2
• Vitamin preparations containing folic acid or its derivatives may decrease responses to methotrexate, though folic acid supplementation is generally recommended to reduce toxicity 2