Standard Methotrexate Dosing by Age Group
Methotrexate dosing varies by indication (e.g., rheumatoid arthritis, cancer, psoriasis) and patient age, with specific limits for children, adults, and older patients to minimize toxicity risks like bone marrow suppression and organ damage. Pediatric doses are typically weight- or body surface area (BSA)-based, capped to avoid overdose.
How Dosing Works for Children Under 18
For juvenile idiopathic arthritis (JIA), the American College of Rheumatology recommends 10-15 mg/m²/week orally or subcutaneously, not exceeding 25 mg/week. In acute lymphoblastic leukemia (ALL) maintenance, doses range from 15-30 mg/m²/week, adjusted by age protocol (e.g., lower in infants under 1 year due to immature clearance). Doses under 2 years often start at 5-10 mg/m² to account for renal immaturity.[1][2]
Adult Dosing Limits and Adjustments
Adults with rheumatoid arthritis receive 7.5-25 mg/week (oral, IM, or SC), with a hard cap at 25 mg/week to prevent hepatotoxicity. Psoriasis dosing is similar, up to 25-30 mg/week. High-dose regimens for cancer (e.g., osteosarcoma) can reach 12 g/m² but require leucovorin rescue; weekly low-dose caps remain at 30 mg.[3]
Adjustments for Elderly Patients Over 65
No strict upper age-specific cap exists, but guidelines mandate 25-50% dose reductions for renal impairment (common in elderly, CrCl <60 mL/min). Start at 7.5 mg/week for RA, monitor closely for cytopenias. FDA labeling notes increased toxicity risk without numeric age limits.[4]
Renal and Hepatic Factors Overriding Age
Age interacts with kidney function; doses drop 50% if CrCl 30-60 mL/min, avoided if <30 mL/min. Hepatic fibrosis risk limits cumulative lifetime exposure, regardless of age.[1][3]
Common Overdose Risks by Age
Pediatric errors often exceed 25 mg/week due to miscalculated BSA; adults risk high-dose confusion with weekly low-dose. Symptoms include mucositis and pancytopenia, treated with glucarpidase for high levels.[2]
[1]: FDA Methotrexate Label
[2]: UpToDate: Methotrexate in JIA
[3]: Lexicomp: Methotrexate Dosing
[4]: ACR RA Guidelines 2021