What are the potential side effects of Methotrexate (methotrexate) and how can they be managed in patients with rheumatoid arthritis or psoriasis?

Methotrexate Side Effects and Management

Methotrexate causes common gastrointestinal toxicity (nausea, anorexia, stomatitis), hematologic suppression, and hepatotoxicity, with rare but serious risks of pneumonitis and infection; these effects are managed through dose adjustment, route changes, folic acid supplementation, and rigorous laboratory monitoring. 1, 2

Common Side Effects (Occur Early in Treatment)

Gastrointestinal toxicity is the most frequent adverse effect: 1, 3

• Nausea, vomiting, anorexia 1, 2
• Stomatitis (mouth ulcers) 1, 2
• Diarrhea 2
• Management: Change from oral to subcutaneous/intramuscular route, split weekly dose into three divided doses over 24 hours, or take medication with food 1

Constitutional symptoms: 1

• Fatigue and malaise 1, 2
• Chills and fever 2

Minor hepatic enzyme elevations occur commonly and require monitoring but are not necessarily dangerous: 2

• If AST/ALT < 2-fold upper limit of normal: repeat in 2-4 weeks 2
• If 2-3 fold elevated: closely monitor, repeat in 2-4 weeks, decrease dose 2
• If > 3-fold elevated: consider dose reduction 2
• If > 5-fold elevated: discontinue methotrexate 2

Serious Side Effects Requiring Immediate Action

Bone marrow suppression (pancytopenia, anemia, leukopenia, thrombocytopenia): 1, 2, 4

• Can occur after even a single dose 2
• Risk factors: advanced age, renal impairment, lack of folic acid supplementation, drug interactions, hypoalbuminemia 2
• Monitoring: CBC with differential weekly for first 6 months, then every 1-3 months 2
• Management: If suspected, administer folinic acid 10 mg/m² immediately, then every 6 hours 2

Hepatotoxicity (fibrosis, cirrhosis): 5, 1, 2

• Less common than initially reported, particularly with modern dosing regimens 2
• Risk factors: alcohol consumption, obesity, diabetes, hyperlipidemia, hepatitis B/C, concomitant hepatotoxic drugs 2
• For patients WITHOUT risk factors: 2
  • No baseline liver biopsy needed 2
  • Monitor liver function tests monthly for 6 months, then every 1-3 months 2
  • Consider liver biopsy after 3.5-4.0 g cumulative dose (not 1.0-1.5 g as previously recommended) 2
• For patients WITH risk factors: 2
  • Consider baseline liver biopsy after 2-6 months to establish efficacy first 2
  • Repeat liver biopsies after 1.0-1.5 g cumulative dose 2

Interstitial pneumonitis (rare but potentially fatal): 1, 2

• More common in rheumatoid arthritis than psoriasis 1
• A meta-analysis found no significant increase in respiratory infections or adverse respiratory events (RR 1.03,95% CI 0.90-1.17) 1
• No pulmonary deaths occurred in systematic review of 1630 participants 1

Infections and reactivation of latent disease: 1

• Tuberculosis reactivation 1
• Hepatitis B/C reactivation 1
• Epstein-Barr virus-associated B-cell lymphoma 1
• Screening required: Hepatitis B/C serology, tuberculosis testing (PPD or QuantiFERON) based on risk factors 1, 2

Less Common Side Effects

• Photosensitivity ("radiation recall") 2
• Alopecia 2
• Dizziness 2
• Epidermal necrolysis 1
• Gastrointestinal ulceration and bleeding 2

Critical Drug Interactions That Increase Toxicity

Avoid or use extreme caution with: 5, 2, 6

• NSAIDs (salicylates, ibuprofen, naproxen, indomethacin): decrease renal elimination of methotrexate 5, 2
• Antibiotics (trimethoprim/sulfamethoxazole, sulfonamides, penicillins, minocycline, ciprofloxacin): increase methotrexate levels 5, 2
• Alcohol: increases hepatotoxicity risk 5, 2
• Other hepatotoxic drugs: statins, leflunomide, retinoids, azathioprine 2
• Diuretics (furosemide, thiazides): decrease renal elimination 2
• Phenytoin, probenecid, colchicine: various mechanisms increasing toxicity 5, 2

Essential Preventive Measures

Folic acid supplementation (1-5 mg daily, except on methotrexate dosing day) reduces side effects without compromising efficacy: 2

• Decreases gastrointestinal symptoms 2
• Reduces hematologic toxicity 2
• Does not interfere with therapeutic effect 2

Baseline screening before initiating methotrexate: 1, 2, 6

• Complete blood count with differential 2, 6
• Liver function tests (AST, ALT, alkaline phosphatase, albumin, bilirubin) 2, 6
• Serum creatinine and BUN (calculate GFR in elderly or those with decreased muscle mass) 2, 6
• Hepatitis B and C screening 1, 2
• Tuberculosis testing (PPD or QuantiFERON) based on risk factors 1, 2
• Pregnancy test in women of childbearing potential 2, 4

Test dose protocol: 2

• Give 2.5-5 mg test dose initially 2
• Check CBC 5-6 days later to ensure no myelosuppression 2
• Mandatory in patients with decreased GFR or significant risk factors 2

Absolute Contraindications

4

• Pregnancy (causes fetal death and teratogenic effects) 4
• Breastfeeding 4
• Alcoholism or alcoholic liver disease 4
• Immunodeficiency syndromes 4
• Preexisting blood dyscrasias (bone marrow hypoplasia, leukopenia, thrombocytopenia, significant anemia) 4
• Known hypersensitivity to methotrexate 4

Pregnancy and Fertility Considerations

Women: 5, 2

• Contraception required during treatment and for at least one ovulatory cycle (3 months) after stopping 5, 2, 4
• Pregnancy must be excluded before starting treatment 4

Men: 5, 2

• Methotrexate causes spermal abnormalities 5
• Contraindicated in men wishing to father children 5
• Wait 3 months after discontinuing before attempting conception (one cycle of spermatogenesis = 74 days) 2

Common Pitfalls to Avoid

• Never prescribe methotrexate without confirming adequate renal function, as 85% is renally excreted and impaired clearance causes severe toxicity 2
• Never combine with trimethoprim/sulfamethoxazole without extreme caution, as this combination precipitates pancytopenia 2, 7
• Never allow patients to take methotrexate daily instead of weekly, as dosing errors cause life-threatening toxicity 2
• Never skip folic acid supplementation, as this simple intervention prevents most common side effects 2
• Do not perform liver biopsies at 1.0-1.5 g cumulative dose in low-risk patients; current evidence supports waiting until 3.5-4.0 g 2