Local anesthetics as antimicrobial agents: a review.

BACKGROUND: Since the introduction of cocaine in 1884, local anesthetics have been used as a mainstay of pain management. However, numerous studies over the past several decades have elucidated the supplemental role of local anesthetics as antimicrobial agents. In addition to their anesthetic properties, medications such as bupivacaine and lidocaine have been shown to exhibit bacteriostatic, bactericidal, fungistatic, and fungicidal properties against a wide spectrum of microorganisms. METHODS: A comprehensive literature search was conducted using MEDLINE 1950-present for in vitro and in vivo studies pertaining to the antimicrobial activity of various local anesthetics on a broad range of bacterial and fungal pathogens. Studies testing the effect on microbial growth inhibition of local anesthetics alone and in combination with other agents, such as preservatives and other medications, as well as the effect of conditions such as concentration and temperature, were included for review. Outcome measures included colony counts, area-under-the-curve and time-kill curve calculations, minimum inhibitory concentrations, and post-antibiotic effect. RESULTS: Evidence suggests that local anesthetics as a class possess inherent antimicrobial properties against a wide spectrum of human pathogens. Multiple local anesthetics at concentrations typically used in the clinical setting (e.g., bupivacaine 0.125%-0.75%; lidocaine 1%-3%) inhibit the growth of numerous bacteria and fungi under various conditions. Different local anesthetics showed various degrees of antimicrobial capacity; bupivacaine and lidocaine, for example, inhibit growth to a significantly greater extent than does ropivacaine. Greater concentrations, longer exposure, and higher temperature each correlate with a proportional increase in microbial growth inhibition. Addition of other agents to the anesthetic solutions, such as preservatives, opioids, or intravenous anesthetics such as propofol, modify the antimicrobial activity via either synergistic or antagonistic action. Limited studies attribute the mechanism of action of antimicrobial activity of local anesthetics to a disruption of microbial cell membrane permeability, leading to leakage of cellular components and subsequent cell lysis. CONCLUSIONS: Local anesthetics not only serve as agents for pain control, but possess antimicrobial activity as well. In such a capacity, local anesthetics can be considered as an adjunct to traditional antimicrobial use in the clinical or laboratory setting. Additionally, caution should be exercised when administering local anesthetics prior to diagnostic procedures in which culture specimens are to be obtained, as the antimicrobial activity of the local anesthetic could lead to false-negative results or suboptimal culture yields.

Improved pain management outcomes with continuous infusion of a local anesthetic after thoracotomy.

OBJECTIVE: We sought to determine the effectiveness of an incisional infusion of local anesthetics through a continuous-infusion elastomeric pump for the management of postoperative pain after thoracotomy. METHODS: We performed a retrospective comparative analysis of 110 patients undergoing thoracotomies between November 1999 and March 2003. Postoperative pain management with a continuous-infusion elastomeric pump providing local anesthetic into the incisional area was compared with a single-shot epidural in combination with continuous local anesthetic infusion and continuous thoracic epidural infusion. Data sources were reviewed for mean narcotic use, pain score, and complications. RESULTS: After thoracotomy procedures, 38 patients received the ON-Q Pain Relief System (I-Flow Corp, Lake Forest, Calif), 32 received the ON-Q device and single-shot epidural infusion, and 40 received continuous epidural infusion. Demographic attributes, including age, body mass index, and sex were similar between the groups. Preoperative American Society of Anesthesiologists status was significantly higher in the ON-Q group compared with that in the other groups (P = .02). Narcotic use and pain scores were significantly reduced in the ON-Q group compared with that in the epidural group at all time points (P < .001). There were no wound-healing complications or infections associated with the use of the pump. CONCLUSION: A continuous infusion of 0.25% bupivacaine at 4 mL/h through the ON-Q elastomeric infusion pump is a safe and effective adjunct in postoperative pain management after thoracotomy. The use of the ON-Q Pain Relief System results in decreased narcotic use and lower pain scores compared with continuous epidural infusion.