Measurement of drug concentration and bacterial contamination after diluting morphine for intrathecal administration: an experimental study
Abstract Background: We did this study to analyse the risks posed by manual diluted morphine solutions intended for intrathecal use. Dilution of morphine is needed to achieve low concentrations for intrathecal injection. Dilution poses the risk of dilution errors and bacterial contamination. The primary goal was to compare the concentrations of morphine and bupivacaine between four groups of syringes. The secondary goal was to investigate the difference in contamination rate between these groups. Methods: 25 experienced anaesthesia providers were asked to prepare a mixture of bupivacaine 2.0 mg/ml and morphine 60 µg/ml using 3 different methods as clean and precise as possible. The fourth method used was the aspiration of ampoules prepared by the pharmacy. The concentrations of morphine and bupivacaine were measured by High-Pressure Liquid Chromatography (HPLC). The medication was cultured for bacterial contamination. Results: Group 1 (60 µg/ml; 95% CI: 59-110 µg/ml) yielded 3 outliers above 180 µg/ml morphine concentration. Group 2 (76 µg/ml; 95% CI: 72-80 µg/ml) and 3 (69 µg/ml; 95% CI: 66-71 µg/ml) were consistently higher than the target concentration of 60 µg. The group “pharmacy” was precise and accurate (59 µg/ml; 95% CI: 59-59 µg/ml). Two groups had one contaminated sample with a spore-forming aerobic gram-positive rod. Conclusion: Manually diluted morphine is at risk for deviating concentrations, which could lead to increased side-effects. Medication produced by the hospital pharmacy was highly accurate. Furthermore, even when precautions are undertaken, contamination of the medication is a serious risk and appeared to be unrelated to the dilution process. Trial registration: Not applicable