Computerized gravimetric control of parenteral analgesic admixtures: A retrospective quality improvement study

Postoperative pain and labor pain are among the most prevalent and intense types of acute pain. Their effective management often requires the administration of parenteral analgesic mixtures combining opioids with local anesthetics. Since no ready-to-use commercial formulations are available and given the complexity and risk of error in their preparation, the Spanish Guide to Good Medication Preparation Practices in Hospital Pharmacy Services recommends their centralized compounding in clean rooms within the pharmacy department. The aim of this study is to describe the implementation experience of a computerized gravimetric control system for stock-prepared analgesic formulations and to assess its reliability and usefulness.

A retrospective observational study was conducted including all analgesic units prepared in the Pharmacy Department between July 2024 and April 2025. Gravimetric control was performed using an electronic balance integrated into the Pharmasuite® software, which automatically calculated the concordance between theoretical and actual weight, generating alerts in case of deviations. Primary acceptance limits were set at ±1.5-1.7% depending on the formulation, based on previous experience and the consistency observed in earlier batches. A total of seven different formulations were analyzed.

During the study period, 1,460 units were prepared, corresponding to 238 batches. Five out of the seven formulations achieved 100% compliance with the acceptance limit. In the remaining formulations, the proportion of non-compliant units was below 1%. The mean relative standard deviation ranged from 0.189% to 0.338%, always below 0.5%, indicating high reproducibility. The mean actual weight was very close to the theoretical weight in all formulations. Units falling outside the acceptance range were individually discarded, and no complete batch had to be rejected.

The implementation of computerized gravimetric control in the compounding of analgesic formulations proved to be an effective and safe strategy to ensure accuracy, detect errors, and reinforce traceability. The experience described represents a quality improvement tool that may be extrapolated to other centers.