Background and Objectives. Local anesthetics inhibit bacteria growth in culture although this effect diminishes as the concentration of the drug is reduced. The antimicrobial properties of opioids are unknown. This study was designed to determine the ability of lidocaine and bupivacaine, with or without fentanyl or sufentanil, to inhibit bacteria growth in culture at concentrations typically used to provide analgesia.

Methods. Potential bacteria pathogens were cultured in agar media containing: agar alone, 2%, 1.5%, and 1% lidocaine, 0.5%, 0.25%, and 0.125% bupivacaine, 0.125% bupivacaine + fentanyl 2 mcgs/mL, 0.125% bupivacaine + sufentanil 0.3 mcgs/mL, and fentanyl 5 mcgs/mL, fentanyl 2 mcgs/mL or sufentanil 0.3 mcgs/mL. Organisms were deemed sensitive to the study agent if no growth was apparent after incubation for 24 hours.

Results. Both lidocaine and bupivacaine significantly reduced bacteria growth at all concentrations studied compared to the growth observed in agar alone (P < .0001). This growth inhibition diminished as the concentration of local anesthetic was reduced especially for certain bacteria species for example. Staphylococcus aureus (P < .0001). Neither fentanyl nor sufentanil inhibited any bacterial growth in culture.

Conclusions. Since the growth in culture of common pathogens, especially S. aureus, is not inhibited as the concentration of local anesthetic is reduced, the local anesthetics tested are unlikely to help prevent epidural-catheter-related infection due to common pathogens. More study is necessary to determine if local anesthetics help prevent infection from less common pathogens in patients at increased risk for infectious complications.