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To assess and compare the growth of four microorganisms in solutions of intravenous anesthetics, known quanta of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans were inoculated into propofol, thiopental, a 1:1 mixture of propofol and thiopental, and normal saline. All microorganisms were taken from standard stock cultures and incubated for 24 h (48 h for C. albicans). Growth of microorganism in each drug was compared by counting the number of colony forming units (CFUs) grown from a subculture of each inoculated anesthetic at 0, 3, 6, 12, and 24 h. The study shows that propofol strongly supports the growth of E. coli and C. albicans but is bacteriostatic toward S. aureus and weakly bactericidal toward P. aeruginosa. In contrast, both thiopental and the 1:1 mixture of propofol and thiopental behaved differently, exhibiting markedly bactericidal properties toward E. coli, S. aureus, and P. aeruginosa and a bacteriostatic effect on C. albicans. This finding supports recommendations that a strict aseptic technique should be used when handling propofol and that the contents of an ampoule should be used within 6 h of aspirating. The measured high pH of both thiopental and the 1:1 mixture of propofol and thiopental compared to propofol alone suggests pH to be a major factor in determining whether a given drug will support microbial growth.

Propofol emulsion supports bacterial growth.Extrinsic contamination of propofol has been implicated as an etiological event in postsurgical infections. When added to propofol, local anesthetics (e.g., lidocaine) alleviate the pain associated with injecting it. Because local anesthetics have antimicrobial activity, we determined whether lidocaine would inhibit microbial growth by comparing the growth of four microorganisms in propofol and in mixtures of propofol and lidocaine. Known quanta of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans were inoculated into solutions of 1% propofol, 0.2% lidocaine in propofol, 0.5% lidocaine in propofol, 0.5% lidocaine in isotonic sodium chloride solution, and 0.9% isotonic sodium chloride solution. All microorganisms were taken from stock cultures and incubated for 24 h. Growth of microorganisms in each solution was compared by counting the number of colony-forming units grown from a subculture of the solution at 0, 3, 6, 12 and 24 h. Propofol supported the growth of E. coli and C. albicans. Propofol maintained static levels of S. aureus and was bactericidal toward P. aeruginosa. The addition of 0.2% and 0.5% lidocaine to propofol failed to prevent the growth of the studied microorganisms. The effect of 0.5% lidocaine in isotonic sodium chloride solution did not differ from the effects of isotonic sodium chloride solution alone. We conclude that lidocaine, when added to propofol in clinically acceptable concentrations, does not exhibit antimicrobial properties. Implications: Local anesthetics such as lidocaine have antimicrobial activity. Propofol supports the growth of bacteria responsible for infection. Bacteria were added to propofol and propofol mixed with lidocaine. The addition of lidocaine to propofol in clinically relevant concentrations did not prevent the growth of bacteria. The addition of lidocaine to propofol cannot prevent infection from contaminated propofol. (Anesth Analg 1999;88:209-12)