Methotrexate Dosing for JIA According to BNFC
For a 7-year-old child with JIA weighing 29.7 kg, the recommended initial methotrexate dose is 10-15 mg/m² body surface area per week, administered orally, which translates to approximately 10-15 mg weekly for this patient's BSA (approximately 1.0 m²). 1
Initial Dosing Strategy
Start with low to intermediate dose methotrexate (10-15 mg/m² BSA per week) for children with low to moderate disease activity without poor prognostic features. 1
The oral route is appropriate for initial therapy at these doses, as no clinically significant differences in efficacy have been demonstrated between oral and parenteral administration at doses below 15 mg/m² BSA per week. 1
For this specific patient with BSA of approximately 1.0 m², the actual weekly dose would be 10-15 mg administered once weekly. 1
Methotrexate is the cornerstone first-line disease-modifying therapy, inducing remission in 60-70% of children with JIA. 1, 2
Route of Administration Considerations
Switch to subcutaneous administration if the dose reaches 15 mg/m² BSA per week or if there is inadequate response to oral therapy. 1
Lower and saturable intestinal absorption may affect oral methotrexate efficacy, particularly in younger patients. 1
Subcutaneous methotrexate at 15 mg/m² BSA per week is associated with high response rates within the first 12 months and low rates of clinically significant adverse effects. 1
The maximum recommended dose is 25 mg weekly via subcutaneous route. 1
Dose Escalation Parameters
Do not exceed 15 mg/m² BSA per week, as higher doses provide no additional therapeutic benefit. 1
A randomized trial of 80 children with JIA demonstrated no additional benefit at doses exceeding 15 mg/m² BSA per week. 1
If inadequate response occurs after 6-8 weeks at optimal dosing, consider switching from oral to parenteral route before escalating to biologic therapy. 1
Disease Activity-Based Approach
For moderate to high disease activity (JADAS-27 >3.9) or presence of poor prognostic features, consider combination therapy with methotrexate 15 mg/m² BSA per week plus a biologic DMARD. 1
Poor prognostic features include: positive anti-CCP antibodies, positive rheumatoid factor, or presence of joint damage. 1
High-risk joint involvement (cervical spine, wrist, or hip) warrants more aggressive initial therapy. 1
Common Pitfalls to Avoid
Do not delay methotrexate initiation while trialing NSAIDs alone—NSAIDs serve only as adjuvant therapy for pain and inflammation. 2, 3
An adequate NSAID trial is 8 weeks, but methotrexate should be started concurrently, not sequentially. 1, 2
Approximately 50% of children develop adverse effects with methotrexate, most commonly gastrointestinal symptoms (35.6%) and behavioral problems (35.6%). 4
Age older than 6 years at therapy initiation increases the risk of developing adverse effects. 4
Switching from oral to subcutaneous route resolves intolerance in approximately 55% of cases. 4, 5
Monitoring and Duration
Continue methotrexate for at least 12 months after achieving inactive disease before considering discontinuation. 1