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Disease-Modifying Antirheumatic / Immunosuppressant

Methotrexate (Dermatology — Psoriasis)

Brand names: Methofar, Methofar XL

Methotrexate is a disease-modifying immunosuppressant taken ONCE A WEEK for psoriasis, rheumatoid and other inflammatory arthritis, and other immune-mediated conditions.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

• Instruct patients and caregivers to take the recommended dosage as directed, because medication errors have led to deaths. (2.1, 5.9) • Verify pregnancy status in females of reproductive potential before starting methotrexate tablets. (4, 5.1) • ALL: The recommended dosage is 20 mg/m 2 orally once weekly as a part of a combination chemotherapy maintenance regimen. (2.2) • Mycosis fungoides: The recommended dosage is 25 to 75 mg orally once weekly as monotherapy; 10 mg/m 2 orally twice weekly as part of combination chemotherapy. (2.2) • Relapsed or refractory non-Hodgkin lymphoma: The recommended dosage is 2.5 mg orally two to four times per week as part of metronomic combination …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2024-06-04. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

At these low doses it inhibits dihydrofolate reductase and other folate-dependent enzymes, producing anti-inflammatory and immunomodulatory effects.

Prescribing in practice

  • It is taken ONCE A WEEK — accidental daily dosing is a recognised cause of fatal toxicity, so the dose, day and tablet strength must be unambiguous and a single low tablet strength used to avoid confusion.
  • Folic acid is taken on a different day; monitor for bone-marrow suppression, hepatotoxicity and pneumonitis.
  • It is teratogenic (reliable contraception required) and interacts dangerously with trimethoprim/co-trimoxazole and with NSAIDs in renal impairment.

Monitoring

Monitor FBC, liver and renal function regularly (more frequently at initiation and after dose changes), and ask about new breathlessness or cough (pneumonitis).

Counselling the patient

  • Take it ONCE A WEEK on the same day — never daily; take folic acid on a different day.
  • Report sore throat, fever, mouth ulcers, breathlessness or unusual bruising.
  • Use reliable contraception, avoid pregnancy, and limit alcohol.

Evidence & guidelines

A first-line conventional DMARD for moderate-to-severe psoriasis and inflammatory arthritis, with strict weekly-dosing safety controls (NICE; MHRA/NPSA alerts).

Reference: BAD Methotrexate Dermatology Guidelines; MHRA MTX Safety; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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