BACTERICIDAL ACTIVITY OF CLINICALLY USED LOCAL-ANESTHETICS ON STAPHYLOCOCCUS-AUREUS

Background and Objectives. The rate of onset of antimicrobial activity of local anesthetics is unknown. Similarly, whether the activity is b actericidal or bacteriostatic is also unknown. The antimicrobial activ ity of local anesthetics with preservatives has not been studied. This study investigated the rate and potency of the antimicrobial activity of 0.125%, 0.25%, and 0.5% bupivacaine, 2.0% mepivacaine and 2.0% lid ocaine with preservatives, and 2.0% lidocaine without preservatives on two strains of methicillin-resistant Staphylococcus aureus. Methods. The pathogen was exposed to each local anesthetic for 1, 3, 6, 12, and 24 hours at room temperature. The inocula from these suspensions were diluted to 1:1,000 with physiological saline to inactivate the antimi crobial activity of the local anesthetics and then were cultured for 2 4 hours at 37 degrees C on agar plates. Results. Lower colony counts w ere observed with a 3-hour or longer exposure to 0.5% bupivacaine in b oth strains of S. aureus (P <.05). The 3-hour exposure reduced the cou nt by approximately 60%, the 6-hour exposure by 70%, and the 24-hour e xposure by more than 99%. The bactericidal activity was lowest with 0. 125% bupivacaine and 2.0% mepivacaine. Conclusions. Antimicrobial acti vity was observed shortly after exposure of S. aureus to local anesthe tics and appeared to be bactericidal rather than bacteriostatic. Howev er, the observed bactericidal activity, although it developed rapidly, may be insufficient to account for the low incidence of epidural infe ction related to epidural cannulation.