Medication Administration

Introduction to Methotrexate

Methotrexate is a medication with varying bioavailability depending on the route of administration, with subcutaneous/IM administration providing more consistent bioavailability than oral dosing, as recommended by the European League Against Rheumatism 1

The initial dose of methotrexate in healthy adults should be 5-15 mg weekly, with the option to gradually increase the dose up to a maximum of 25 mg weekly if needed, and should be taken once weekly on the same day each week, as recommended by the British Journal of Dermatology guidelines 2
For pediatric patients ages 13 years and older of average weight, adult dosing principles can be applied, with a maximum dose of 25 mg/week, according to the Journal of the American Academy of Dermatology 3
A specific dosing example is 10.8 mg weekly for a 54 kg patient, calculated at 0.2 mg/kg body weight, with a maximum dose not exceeding 0.2 mg/kg body weight, as per the British National Formulary for Children (BNFC) and the British Medical Journal 4

Laboratory tests should be performed 4-6 days after dosing, and initial monitoring should include blood tests every 7-14 days for the first month, with ongoing monitoring including blood tests every 2-3 months once therapy is stabilized, as recommended by the Journal of the American Academy of Dermatology and the British Journal of Dermatology guidelines 3, 2
Liver monitoring should include checking PIIINP every 3 months for patients with psoriasis, as recommended by the British Journal of Dermatology guidelines 2

Folate supplementation must be prescribed alongside methotrexate to reduce toxicity, typically at a dose of 5 mg weekly or 1 mg daily, except on methotrexate day, with a strong recommendation and Grade A evidence, as recommended by the British Journal of Dermatology and other guidelines 2, 5, 6
Drug interactions that increase methotrexate toxicity include NSAIDs, certain antibiotics, proton pump inhibitors, salicylates, statins, and alcohol, as reported by the British Medical Journal and the British Journal of Dermatology guidelines 4, 2

Methotrexate is contraindicated in patients with pregnancy or breastfeeding, significant hepatic damage, anemia, leucopenia, or thrombocytopenia, as stated in the British Medical Journal 4
Patients should restrict alcohol intake to minimize the risk of hepatotoxicity, and methotrexate is absolutely contraindicated during pregnancy, with effective contraception essential, as recommended by the British Journal of Dermatology guidelines 2

Patients should seek urgent medical care if they develop symptoms such as fever, mouth ulceration, unusual fatigue, unexplained bruising or bleeding, nausea, vomiting, abdominal pain, dark urine, breathlessness, or cough, as recommended by the British Journal of Dermatology guidelines 2
The American Academy of Dermatology recommends that patients should continue treatment for at least 12-16 weeks before determining efficacy, as therapeutic benefit may not be apparent for 3-12 weeks, with a recommendation to take methotrexate ONCE WEEKLY, not daily, to prevent fatal toxicity 2, 7