Antibacterial activity of local anesthetics against multidrug-resistant bacteria in vitro.

Objectives: Local anesthetics are widely used in clinical settings for pain management. In addition to their analgesic effects, they may also exhibit antimicrobial properties. However, data on their activity against multidrug-resistant (MDR) pathogens are limited. This study aimed to evaluate the in vitro antibacterial activity of lidocaine, levobupivacaine, and bupivacaine against MDR bacteria, including Pseudomonas aeruginosa (MRPA), carbapenem-resistant Enterobacterales (CRE), and Acinetobacter baumannii (MRAB).

Methods: The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of each anesthetic were determined using the standardized broth microdilution method according to CLSI guidelines. Clinical isolates of MRPA, CRE, and MRAB were tested. Identification was performed using MALDI-TOF MS and VITEK II systems. The local anesthetics were diluted to clinically relevant concentrations and tested in duplicate.

Results: Bupivacaine exhibited the strongest antimicrobial activity, with MICs of 1.6 mg/mL for MRAB and 3.2 mg/mL for CRE. Lidocaine showed limited activity, with an MIC of 16 mg/mL for MRPA. Levobupivacaine showed intermediate effects. In all cases, MBCs were higher than the corresponding MICs. These findings suggest differential antibacterial efficacy among the agents.

Conclusions: Local anesthetics demonstrated measurable antibacterial effects against MDR pathogens in vitro. Bupivacaine showed the strongest activity but has a lower clinical dosage limit due to its cardiotoxicity. While lidocaine has weaker antibacterial potency, its widespread use and safety profile make it a practical option. These results suggest local anesthetics may play a complementary role in infection-prone procedures but require cautious interpretation for clinical application.