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Obviously, the concern for using topical anesthetics prior to collecting specimens for microbiology cultures is that the agent might have antibacterial activity. While I am not personally familiar with the antimicrobial activity of many agents, at least one study has been performed for lidocaine in particular which is shown below. To be conservative, however, it would be better not to introduce topical agents for use prior to drawing blood for culture and if it is used, it would probably be a good idea to remove as much as possible before venepuncture.
1: Wound Repair Regen. 2006 Sep-Oct;14(5):581-5. Links
Antibacterial properties of EMLA and lidocaine in wound tissue biopsies for culturing.Berg JO, Mossner BK, Skov MN, Lauridsen J, Gottrup F, Kolmos HJ.
Department of Plastic Surgery, University Center of Wound Healing, Odense University Hospital, Odense, Denmark. joberg@dadlnet.dk
If a tissue biopsy from a chronic wound is sampled for culture, the antibacterial properties of local anesthetics may pose a problem in producing false-negative results. The purpose of this study was to investigate the effects of EMLA (AstraZeneca) and lidocaine on common wound pathogenic bacteria. An in vitro study of a total of 25 clinical isolates and ATCC reference strains of Staphylococcus aureus (including methicillin-resistant S. aureus), Escherichia coli, Pseudomonas aeruginosa, and Streptococcus pyogenes was conducted. The isolates were exposed to the local anesthetic drugs (and some of their contents separately) at 35 degrees C over a 24-hour period and time-kill curves were recorded. No culture media were used and saline was used for controls. EMLA was found to have a rapid acting and powerful antibacterial effect and should not be used before culturing tissue samples. Lidocaine 1% was found not to inhibit the bacterial strains when exposure time was held below 2 hours. We conclude that culturing tissue from a wound biopsy is safe within 2 hours when a pure, preservative-free lidocaine 1% solution is used.
PMID: 17014670 [PubMed - indexed for MEDLINE]
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