The chemical stability and sterility of sodium thiopental after preparation

Manufacturer's instructions recommend discarding unused portions of sodium thiopental 24 h after reconstitution. Heeding this recommendation may result in the disposal of a large proportion of prepared thiopental. Although thiopental is relatively inexpensive, the volume prepared by many anesthesia departments could make this waste significant. To address this possibility, we investigated the chemical stability and sterility of thiopental in pharmacy-prepared, prefilled syringes. Stock solutions of thiopental were mixed and drawn into syringes under sterile conditions by pharmacists or pharmacy assistants. Fifty-six samples were stored under refrigeration (3°C); the remaining 56 samples were stored at room temperature (22°C). Each day for 7 days, eight samples from each group were analyzed by using high-performance liquid chromatography for chemical stability and cultured for microbiological colonization. Differences in thiopental concentration between the room temperature and the refrigerated samples were measured over time by using repeated-measures analysis of variance (P ≤ 0.05). Three positive culture samples (S. epidermidis and S. hemolyticus) most likely represent laboratory contamination and not colonization. At 22°C, thiopental remains stable and sterile for 6 days and wellbeyond 7 days at 3°C. Implications: This study examines the shelf life of the anesthetic drug thiopental in pharmacy-filled syringes stored at either room temperature or under refrigeration. The results justify the use of prepared solutions beyond the package insert recommendation of 24 h.