Novel weighing approach for improved management of methadone stock inventory

Current inventory tracking methods may not be sufficiently accurate. To develop a novel weighing method to improve management of methadone stock inventory. This study used a novel weighing approach to address deficiencies in methadone inventory management. Data on purchased volume, prescribed volume, and methadone inventory were collected from eight drug addiction treatment centres (DATCs) in Tainan, Taiwan, from 2017 to 2022. Descriptive pre–post comparisons were conducted to evaluate changes in inventory surplus ratios before (2017–2019) and after (2020–2022) implementation of the weighing approach. Annual methadone surplus ratios were calculated to evaluate the effectiveness of the novel weighing approach. The novel weighing algorithm comprised device calibration and pre-weighing preparations, recording utensil and drug weights at dispensation and after administration, calculating actually consumed volume from weight and density, comparing this with the prescribed volume, and updating inventory data for any surplus or deficit and remaining stock volume. Before intervention, the 8 DATCs reported an inventory surplus of 4.46 L, which increased to 17.77 L post-intervention. Annual inventory surplus ratios ranged from 0.11% to 0.13% before implementation and were 0.20%, 0.74%, and 0.98% in 2020, 2021, and 2022, respectively. This increase may reflect systematic measurement differences between weight-based and conventional volumetric methods. The proposed novel weighing approach showed potential for improving the detection and documentation of inventory discrepancies and enhancing inventory accounting transparency.