What is the methotrexate dose for a 54 kg patient using BNFC guidelines?

Methotrexate Dosing for a 54 kg Patient According to BNFC Guidelines

For a 54 kg patient, the appropriate methotrexate dose according to BNFC guidelines is 15 mg weekly (oral, subcutaneous, or intramuscular), with a maximum of 25 mg weekly. 1

Dosing Calculation and Administration

The British National Formulary for Children (BNFC) recommends methotrexate dosing for psoriasis and other inflammatory conditions as follows:

• Standard dosing: 15 mg weekly as a single dose 1
• Maximum dosing: 25 mg weekly 1
• Administration routes: oral, subcutaneous, or intramuscular 1

For a 54 kg patient, the standard 15 mg weekly dose is appropriate to start with. This aligns with the BNFC recommendation for standard systemic therapy in psoriasis.

Body Surface Area (BSA) Considerations

While some guidelines suggest BSA-based dosing, particularly for pediatric patients, the BNFC provides weight-based guidance for methotrexate. For reference:

• For pediatric patients with juvenile idiopathic arthritis, doses between 10-15 mg/m² BSA per week are recommended 1
• If using BSA-based dosing and the dose reaches 15 mg/m² BSA per week, switching to the parenteral route (subcutaneous) is advised 1

Dosing Schedule Options

There are two main dosing schedules:

1. Single weekly dose: 15 mg once weekly (preferred method) 1
2. Divided dose: 2.5 mg at 12-hour intervals for 3 doses given as a course once weekly 1

Important Administration Considerations

• Folic acid supplementation: Should be given daily except on the day methotrexate is administered to reduce side effects 1, 2
• Route conversion: If gastrointestinal side effects occur with oral administration, consider switching to subcutaneous administration at the same weekly dose 1, 2
• Monitoring: Regular blood tests (CBC, liver function, renal function) should be performed every 1-1.5 months when starting treatment 2

Dose Adjustment Considerations

• If inadequate response after 4-8 weeks, dose may be increased gradually up to the maximum of 25 mg weekly 1
• If liver enzymes are ≥3× upper limit of normal for 2 consecutive months, methotrexate should be temporarily discontinued 1
• For patients with decreased renal function, dose reduction may be necessary 1

Safety Precautions

• Pregnancy prevention is essential due to teratogenicity risk 1
• Avoid NSAIDs during methotrexate therapy due to potential drug interactions 1
• Monitor for signs of bone marrow suppression, hepatotoxicity, and pulmonary toxicity 1

This dosing recommendation follows the BNFC guidelines for methotrexate in inflammatory skin conditions and provides a safe starting point for treatment while allowing for dose adjustments based on clinical response and tolerability.