Methotrexate Dosing for Psoriasis
For adults with plaque psoriasis, start methotrexate at 7.5-15 mg weekly (oral or subcutaneous), titrate based on response up to a maximum of 25 mg weekly, and always co-prescribe folic acid supplementation. 1
Initial Dosing Strategy
The most recent high-quality guidelines provide clear direction on starting doses:
- Starting dose: 7.5-15 mg weekly is the recommended range 1
- Route of administration: Either oral or subcutaneous (subcutaneous may have better absorption and fewer GI side effects) 1
- Dosing schedule: Can be given as a single weekly dose OR divided into 3 doses over 24 hours 1
Test Dose Consideration
A test dose of 2.5-5 mg should be considered, particularly in patients with:
- Impaired kidney function 1
- Significant comorbidities (diabetes, potential drug interactions) 1
- Elderly patients
After the test dose, check CBC 5-7 days later to assess bone marrow sensitivity 1. However, it's also reasonable to start directly at therapeutic doses (15 mg weekly) in low-risk patients 1.
Dose Titration
Titration approach:
- If starting at 15 mg weekly and inadequate response at week 8, increase to 20 mg weekly 1
- Maximum dose: 25 mg weekly (do not exceed 30 mg/week) 1, 2
- Allow at least 4 weeks between dose adjustments as clinical response takes time 1
Expected timeline for response:
- Therapeutic benefit may not appear for 3-12 weeks 3
- Assess response at 12-16 weeks before considering treatment failure 3, 1
Recent evidence shows that patients achieving PASI 50 by week 8 on 15 mg weekly have good outcomes; those not responding by week 12 despite dose escalation are unlikely to achieve adequate control 4.
Folic Acid Supplementation
Folic acid is mandatory to reduce GI and hepatic adverse effects 1:
- Dose: 5 mg weekly (or daily dosing on non-methotrexate days) 1, 5
- Do NOT give folic acid on the same day as methotrexate to avoid reducing efficacy 1
- Folinic acid is equally effective but more expensive 1
Route-Specific Considerations
Subcutaneous administration advantages:
- Better bioavailability at higher doses
- Fewer GI side effects 1
- May be preferred at doses ≥15 mg weekly
The METOP trial demonstrated that subcutaneous methotrexate at 17.5-22.5 mg weekly achieved 41% PASI 75 at week 16 with favorable safety profile 5.
Monitoring Requirements
Initial monitoring (first month):
- CBC, liver function tests (LFTs), and renal function every 7-14 days 3
Maintenance monitoring:
- CBC, LFTs, renal function every 2-3 months once stable 3
- Liver function tests every 3-6 months if no abnormalities 1
Baseline assessments before starting:
- Noninvasive liver fibrosis assessment (not biopsy) 1
- Screen for hepatitis B and C 1
- Assess alcohol use and other hepatotoxicity risk factors 1
Critical Safety Points
Absolute contraindications:
- Pregnancy (teratogenic - wait 3 months after stopping before conception) 1
- Cirrhosis, significant cytopenias 1
- Active infection 2
Dose adjustments needed for:
- Renal impairment: Lower starting doses (2.5-5 mg weekly) if creatinine clearance reduced 3
- Elderly patients: Consider dose reduction due to decreased CSF volume/turnover 2
Patient warnings:
- Weekly dosing only (not daily) - emphasize this repeatedly 3
- Seek urgent care for: fever, mouth ulcers, unexplained bruising/bleeding, severe nausea, breathlessness 3
- Limit alcohol intake (>1 drink/day for women, >2 drinks/day for men increases hepatotoxicity risk) 1
- Pneumococcal vaccine and annual influenza vaccination recommended 3
When to Discontinue or Switch
Consider alternative therapy if:
- Minimal efficacy after 12-16 weeks at adequate doses 3
- Persistent elevation in liver enzymes despite dose adjustment 1
- Intolerable side effects despite folic acid supplementation
- Patient unable to comply with monitoring requirements 3
Common Pitfalls to Avoid
- Daily dosing error: Methotrexate must be weekly, not daily (daily dosing shows less benefit and more liver toxicity) 1
- Inadequate folic acid: Always prescribe folic acid supplementation 1
- Premature discontinuation: Allow 12-16 weeks before declaring treatment failure 3, 1
- Ignoring renal function: Dose reduction essential in renal impairment 3
- Inadequate contraception counseling: Methotrexate is highly teratogenic 1