Folate antagonist / DMARD / antineoplastic

Methotrexate

Brand names: Maxtrex, Metoject, Nordimet, Zlatal

Adult dose

Dose: RA / psoriasis / Crohn's: 7.5–25mg ONCE WEEKLY PO/SC. Co-prescribe folic acid 5mg weekly (different day). Oncology: specialist

Route: PO/SC/IV/IM/Intrathecal

Frequency: WEEKLY

Dose adjustments

Renal

Reduce in renal impairment; avoid eGFR <30 (rheumatology dose) without specialist input

Clinical pearls

WEEKLY dosing — never daily (NPSA Patient Safety Alert; deaths from inadvertent daily dosing)
Folic acid 5mg ONCE weekly (different day)
Stop pre-op for major surgery; restart when wound healing established

Contraindications

Severe renal/hepatic impairment
Severe myelosuppression
Active severe infection
Pregnancy / breastfeeding (avoid in both partners 6 months pre-conception)
Active peptic ulcer
Severe ascites/pleural effusion

Side effects

Bone marrow suppression
Hepatotoxicity / cirrhosis
Pulmonary toxicity (pneumonitis)
Mucositis
GI upset
Nephrotoxicity (high-dose)
Severe skin reactions

Interactions

NSAIDs (reduce excretion — minor at low rheumatology doses)
Trimethoprim/co-trimoxazole (severe myelosuppression — avoid)
Penicillins (raised levels)
Probenecid
Live vaccines

Monitoring

FBC, U&E, LFTs every 2–4 weeks initially, then 2–3 monthly
Pulmonary symptoms
Pregnancy testing

Reference: BNF; NICE NG100; BSR guidelines; NPSA Patient Safety Alert; https://bnf.nice.org.uk/drugs/methotrexate/. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways