Small-Count Suppression Substantially Distorts Estimates of Pediatric Opioid Utilization in Japan

Effective pain management is essential for pediatric care. However, nationwide trends in pediatric opioid prescribing in Japan remain unclear because publicly available databases suppress small prescription quantities. This study aimed to evaluate how small-count suppression influences the interpretation of pediatric opioid utilization estimates based on the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB Open Data), with the secondary objective of describing nationwide prescribing trends. The NDB Open Data from fiscal years (FY) 2018-2023 were analyzed for children aged 0-14 years. Oral, transdermal, and suppository formulations of morphine, oxycodone, fentanyl, and tramadol were included; injectable formulations were excluded. Opioid utilization was converted to morphine milligram equivalents (MME) per 100,000 population. Prescription quantities below 1,000 units were coded as nondisclosure (ND) and treated as zero in the primary analysis. Sensitivity analyses imputed ND values using the estimated mean MME per reported unit. The suppression rate was defined as the proportion of strong opioid formulation categories with suppressed values. The suppression rate for the strong opioid formulation categories progressively increased and reached 100% in FY2023, indicating a substantial loss of observable prescription data. Sensitivity analyses demonstrated a 4.9-fold difference between the observed and imputed estimates in FY2022. In the primary analysis, estimated pediatric opioid utilization appeared to decrease from 1826 to 346 mg MME/100,000 population between FY2018 and FY2023. Small-count suppression materially distorted estimates of pediatric opioid utilization derived from the NDB Open Data and may complicate the interpretation of prescribing trends in rare pediatric populations.