What is the recommended dose of Methotrexate (MTX) for a 30 kilogram pediatric patient with Juvenile Idiopathic Arthritis (JIA)?

From the Guidelines

For a 30 kg pediatric patient with juvenile idiopathic arthritis (JIA), the recommended starting dose of methotrexate is 0.5-1 mg/kg/week, with a maximum of 30 mg per week, as stated in the childhood arthritis and rheumatology research alliance consensus treatment plans 1. The medication can be administered orally or subcutaneously, with subcutaneous administration often preferred for better absorption and potentially fewer gastrointestinal side effects.

• Key considerations for methotrexate therapy include:
  • Dosing: 0.5-1 mg/kg/week, with a maximum of 30 mg per week
  • Administration: oral or subcutaneous
  • Monitoring: complete blood count, liver function tests, and renal function at baseline and regularly throughout treatment
  • Common side effects: nausea, mouth sores, and elevated liver enzymes
  • Folic acid supplementation: 1 mg daily to reduce side effects The American College of Rheumatology also conditionally recommends using methotrexate over leflunomide or sulfasalazine for JIA treatment 1.
• It is essential to note that the dose may be gradually increased if needed for adequate disease control, with close monitoring. Methotrexate works as an immunomodulator by inhibiting dihydrofolate reductase and promoting adenosine release, thereby reducing inflammation in JIA.
• Patients should be instructed to avoid alcohol and limit sun exposure while on methotrexate therapy. Consensus was reached that 3 months of treatment is necessary before assessing methotrexate efficacy, and patients who failed methotrexate are recommended to change to the TNFi CTP 1.

From the FDA Drug Label

2.11 Recommended Dosage for Polyarticular Juvenile Idiopathic Arthritis The recommended starting dosage of Methotrexate Injection is 10 mg/m2 once weekly administered subcutaneously or intramuscularly, with escalation to achieve optimal response. For a 30 kg pediatric patient, the body surface area (BSA) needs to be calculated to determine the dose. However, assuming an average BSA of 1.07 m2 for a 30 kg child, the dose would be approximately 10 mg/m2 x 1.07 m2 = 10.7 mg. Given the provided information, the recommended dose for a 30 kg pediatric patient with JIA is approximately 10 mg once weekly, administered subcutaneously or intramuscularly, with escalation to achieve optimal response, not to exceed 30 mg/m2 per week 2.

From the Research

Methotrexate Dosing for Pediatric Patients with JIA

• The recommended starting dose of methotrexate for pediatric patients with JIA is 10-15 mg/m²/week orally 3, 4.
• For a 30 kg pediatric patient, the dose can be calculated as follows:
  • Body surface area (BSA) can be estimated using the Mosteller formula: BSA (m²) = √((height (cm) x weight (kg)) / 3600)
  • Assuming an average height for a 30 kg child, the BSA can be estimated to be around 1.1-1.2 m²
  • The starting dose would be 10-15 mg/m²/week, which translates to approximately 11-18 mg/week for a 30 kg child
• The dose of parenteral methotrexate can be increased to 15-20 mg/m²/week 3.
• It is recommended to initiate treatment with a dose of 10-15 mg/m²/week and adjust as needed based on the patient's response and tolerance 4.

Administration and Monitoring

• Methotrexate can be administered orally or parenterally, with parenteral administration preferred for doses ≥15 mg/m²/week 4.
• Regular monitoring of blood counts, liver enzymes, and serum creatinine is necessary to assess potential adverse effects 3, 4.
• Folic or folinic acid may be added to reduce the risk of adverse effects 3, 4.

Clinical Considerations

• Methotrexate is recommended as the first-line disease-modifying antirheumatic drug (DMARD) for pediatric patients with JIA 5, 4.
• Combination therapy with biological agents may be necessary in some cases 5, 6, 4.