Medication Preparation Errors Involving Very Small and Difficult-to-measure Volumes in a Pediatric Hospital: A 14-year Descriptive Study.

PURPOSE: Medication preparation errors are a major source of preventable harm in pediatric hospitals. Oral liquid medications, especially those involving difficult-to-measure or very small volumes, may increase the risk of such errors, yet supporting evidence is limited. This study aims to determine whether difficult-to-measure and very small oral liquid medication volumes are associated with higher rates of preparation errors in a pediatric hospital pharmacy. METHODS: We conducted a retrospective cohort study of all oral liquid medication preparations produced between January 2010 and December 2023 at a tertiary pediatric hospital. Preparation errors identified by pharmacists were extracted from the pharmacy department's workflow management system. A prospective substudy (December 2023-October 2024) was also carried out to characterize the nature and magnitude of rejected preparations. RESULTS: During the study period, 1,554,986 oral liquid preparations were produced. Difficult-to-measure and very small volumes accounted for 20.4% and 1.4% of preparations, respectively. The overall preparation error rate was 0.9%. Error rates were significantly higher for difficult-to-measure (1.4%) and very small volumes (2.0%) compared to other volume types (p < 0.001). In the prospective substudy (N = 911), 65% of rejected preparations involved inaccurate volumes, with high-magnitude errors disproportionately linked to difficult-to-measure and very small volumes. CONCLUSION: Difficult-to-measure and very small volumes significantly increase the risk of preparation errors. Volume rounding, standardized concentrations, and age-appropriate formulations should be prioritized to improve pediatric medication safety.