Background and objective: The intravenous anaesthetic propofol may become contaminated once the ampoules have been opened. The effect of lidocaine and cooling was tested on the bacterial contamination of propofol.

Methods: The study was performed in two parts. In Part 1, 1920 aliquots of propofol alone, and of a propofol-lidocaine mixture, were drawn into sterile syringes and stored at room temperature (24–26°C) or in the refrigerator (12–14°C). In Part 2, 1200 aliquots from opened ampoules of propofol alone, or as a propofol-lidocaine mixture, were stored at room temperature or in the refrigerator. Samples were aerobically cultured at 0, 1, 2, 4, 8, and 12 h.

Results: In Part 1, diphtheroid bacillus was isolated from one aliquot (0.06%). In Part 2, there was bacterial growth in both groups; the number of contaminated ampoules increased with time and it was 20–26% at 12 h. Diphtheroid bacilli and coagulase-negative staphylococci were the most frequent micro-organisms.

Conclusions: When propofol is stored in opened ampoules, the bacterial contamination rate is high. Adding lidocaine, or storing opened ampoules at 12–14°C, does not affect the contamination rate, except during the first few hours. It is advisable to draw propofol aseptically into a syringe in an amount that can be used during one procedure.