BRIEF REPORT Bacterial Growth in Ropivacaine Hydrochloride Istvan Ba ´tai, PhD*, Monika Kere ´nyi, MD†, Judit Falvai*, and Gyorgy Szabo ´, PhD‡ *Department of Anesthesia and Intensive Care, †Department of Clinical Microbiology, ‡Department of Orthopedic Surgery, University of Pe ´cs, Pe ´cs, Hungary D rugs used in anesthesia may influence bacterial growth (1). Used ampules and syringes may be contaminated in a busy environment (2). Epi- dural space infection in association with epidural an- esthesia is rare. The antibacterial effects of local anes- thetics themselves may contribute to this infrequent incidence. A local anesthetic was first reported to kill bacteria in 1909 (3). Since then antibacterial activity of other local anesthetics has been confirmed (1) but there is no study on the effect of undiluted ropivacaine on bacterial growth at room temperature. We investi- gated the effect of ropivacaine 2 mg/mL and 10 mg/mL on bacterial growth. Materials and Methods Bacterial strains were isolates of Staphylococcus aureus (ATCC 23923), and Escherichia coli (ATCC 25922). The tested pharmaceutical preparations were ropivacaine hydrochloride 2 mg/mL and 10 mg/mL (Naropin ® , AstraZeneca, Macclesfield, UK). Mueller-Hinton broth (Oxoid) and saline 0.9% controls were also applied to assess bacterial viability. The method is described in detail elsewhere (4). Mueller-Hinton broth (Oxoid) was inoculated with each organism and incubated overnight at 37°C. The cultures were diluted to a density of 0.5 McFarland units (1.5  10 8 /mL) with sterile nonbacteriostatic saline 0.9%. Each bacterium solution was further di- luted to an approximate initial concentration of 10 3 colony forming units (cfu)/mL. The final concentra- tion of ropivacaine was 1.98 mg/mL and 9.90 mg/mL. Five vials of each tested drug and control were inoc- ulated. After inoculation the culture vials were incu- bated at 20°C and 37°C. Each vial was vortexed and a 10 L sample was then removed and plated on Mueller-Hinton agar (Oxoid) at the following times after inoculation: 0, 3, 6, 12, and 24 h. The plates were then incubated at 37°C for 24 h. The numbers of cfu were counted. The results are expressed as mean  sd. Statistical analysis was performed by using analysis of variance. Individual comparisons between group means were made by using the Scheffe ´ test. P  0.05 was regarded as significant. Results Both strains grew in Mueller-Hinton broth at both 20°C and 37°C. S. aureus did not multiply in saline, although E. coli grew in this control. These results showed the normal growing pattern in these controls. S. aureus did not multiply in ropivacaine 2 mg/mL or 10 mg/mL at room temperature. At 37°C the 2 mg/mL solution reduced its cfu; ropivacaine 10 mg/mL killed it after 6 h (Table 1). E. coli grew in ropivacaine 2 mg/mL at both temperatures. This strain did not multiply in the 10 mg/mL solution at room temperature, and its cfu was reduced after 6 h at 37°C (Table 2). Discussion Our data suggest that although ropivacaine 10 mg/mL inhibits bacterial growth, E. coli grows in ropivacaine 2 mg/mL. When ropivacaine inhibited bacterial growth, it was more evident at 37°C than at 20°C. This effect of temperature is in accordance with previous studies ex- amining the effects of anesthetics on bacteria (1). We evaluated bacterial growth at two different tem- peratures. Concerning infection control, results ob- tained at room temperature should be considered. Intra- or epidural injections and infusions may cause infections if contaminated during their preparation or administration. In a previous study the incidence of contamination of syringes used during epidural anal- gesia was almost 5% (5). The incidence of bacterial contamination of spinal and epidural needles can be as frequent as 17% (6). Bacteria can be introduced into Supported, in part, by Ministry of Health of Hungary Grant Number 385/2000/ETT. Presented, in part, at the 12th World Congress of Anaesthesiolo- gists, June 4-9, 2000, Montre ´al, Canada. Accepted for publication November 6, 2001. Address correspondence to Istvan Ba ´tai, PhD, University of Pe ´cs, Department of Anaesthesia and Intensive Care, Pe ´cs, Szigeti u. 12., H-7624 Hungary. Address e-mail to ibatai@freemail.hu. ©2002 by the International Anesthesia Research Society 0003-2999/02 Anesth Analg 2002;94:729–31 729