Early Nationwide Prescribing of Ultrahigh‐Dose Methylcobalamin for Amyotrophic Lateral Sclerosis in Japan: Comparison With Established Therapies

ABSTRACT Background Treatment options for amyotrophic lateral sclerosis remain limited, and the uptake of newly approved therapies in routine care is poorly characterized. Japan launched ultrahigh‐dose intramuscular methylcobalamin for amyotrophic lateral sclerosis in November 2024. Aim To describe early nationwide methylcobalamin prescription quantities and compare their scale with established amyotrophic lateral sclerosis therapies. Methods We analyzed fiscal year 2024 aggregate prescription quantities from Japan's National Database of Health Insurance Claims and Specific Health Checkups Open Data. Quantities from January through March 2025 were converted to monthly regimen equivalents based on approved dosing schedules. We compared methylcobalamin with oral edaravone and riluzole. We classified prefectures according to whether a positive prescribing quantity was directly disclosed. Results Methylcobalamin prescribing increased from 1142.4 monthly regimen equivalents in January to 1755.5 in March (+53.7%). The calendar‐day‐adjusted increase from February to March was 3.2%. In March, the standardized methylcobalamin volume was 49.5% of oral edaravone volume calculated using maintenance dosing, and at most 35.9% of the total riluzole volume. During fiscal year 2024, positive methylcobalamin quantities were directly reported in 32 of 47 prefectures. The remaining 15 could not be classified because of suppressed cells. Conclusion By March 2025, approximately 4 months after launch, ultrahigh‐dose methylcobalamin prescribing had reached nearly half the oral edaravone maintenance‐regimen‐equivalent volume. These national quantity‐based estimates provide an early benchmark for evaluating subsequent prescribing as more national claims data become available.