Feasibility of a Monthly Morphine Milligram Equivalent Metric for Opioid Surveillance Using the National Claims Database of Japan: A Repeated Cross-Sectional Study in a Low-Consumption Setting.

Japan has very low opioid consumption, yet national data on high-dose dispensing remain scarce. We assessed the feasibility of a monthly morphine milligram equivalent (MME) metric for opioid surveillance using claims data without days' supply information and estimated high-dose dispensing for opioid analgesics potentially compatible with non-cancer pain treatment. Using a repeated cross-sectional analysis of Japan's National Database Sampling Dataset (1% pharmacy claims, 2015-2019), we identified claims for a pre-specified set of strong (e.g., fentanyl, morphine) and weak (e.g., tramadol) opioids. Primary outcomes were proportions of opioid claims exceeding high-dose (≥ 1,800 MME/month, approximately 60 MME/day) and very-high-dose (≥ 2,700 MME/month, approximately 90 MME/day) thresholds. Among 204,159 opioid claims from 18.6 million pharmacy claims, 0.55% of opioid claims (95% confidence interval [CI], 0.52-0.58%; 0.0060% of all pharmacy claims) exceeded the high-dose threshold, and 0.30% of opioid claims (95% CI, 0.28-0.33%) exceeded the very-high-dose threshold. However, high-dose dispensing was highly concentrated among strong-opioid claims (n = 5,353), of which 20.8% and 11.5% exceeded the high-dose and very-high-dose thresholds, respectively; this pattern may partly reflect cancer-related prescribing because indications were unavailable. Weak-opioid monotherapy almost never exceeded thresholds (< 0.01%). Annual proportions showed little temporal change. High-dose opioid dispensing was rare overall in Japan but concentrated within strong-opioid claims. A monthly MME metric may provide a feasible and practical surveillance proxy for identifying high-risk dispensing events in claims databases with limited prescription metadata.