BACTERICIDAL ACTIVITY OF 0.5-PERCENT BUPIVACAINE WITH PRESERVATIVES ON MICROORGANISMS IN THE HUMAN SKIN FLORA

Background and Objectives. The bactericidal activity of 0.5% bupivacai ne with preservatives at body temperature and at room temperature is n ot known. We studied the bactericidal activity of 0.5% bupivacaine wit h 0.08% methyl para-oxybenzoate and 0.02% propyl para-aminobenzoate as preservatives and of the preservatives alone at 37 degrees C and at r oom temperature on two strains of methicillin-resistant Staphylococcus aureus, two strains of methicillin-susceptible S. aureus, and one str ain each of Staphylococcus epidermidis and Escherichia coli. Methods. The pathogen was exposed to 0.5% bupivacaine with preservatives or to the preservatives alone for 1, 3, 6, 12, and 24 hours at 37 degrees C and at room temperature. The inocula from these suspensions were cultu red for 48 hours al 37 degrees C after the antimicrobial activity of b upivacaine was inactivated by 1:1,000 dilution with physiological sali ne. Results. The 1- through 12-hour exposures of four strains of S. au reus to 0.5% bupivacaine with preservatives at room temperature reduce d the mean colony count by 24.2%, 49.2%, 71.3%, and 89.6%, respectivel y, and the exposure at 37 degrees C reduced the count by 74.1%, 95.2%, 99.9%, and 99.8%, respectively. The differences for 1- through 12-hou r exposures were significant (P < .001). The percentage kill in the st rains of E. coil and S. epidermidis was significantly higher than that in the strains of S. aureus at all exposure rimes at room temperature (E. coli, P < .001; S. epidermidis, P < .0001) and at 1- and 3-hour e xposures at 37 degrees C (E. coli, P < .001; S. epidermidis, P < .0001 ). The bactericidal activity of the preservatives was markedly lower t hat that of 0.5% bupivacaine with preservatives (P < .0001). Conclusio ns. The bactericidal activity of 0.5% bupivacaine with preservatives i s stronger at body temperature than at room temperature; the bacterici dal activity may be due, to a large extent, to bupivacaine rather than to the preservatives; and S. aureus is more resistant to the bacteric idal activity of bupivacaine than are S. epidermidis and E. coli.