The antibacterial activity of tramadol against bacteria associated with infectious complications after local or regional anesthesia.

BACKGROUND: Tramadol is a synthetic analog of codeine with opioid and local anesthetic properties. It is used as a central-acting analgesic, and recently, in subcutaneous or intradermal injections, as a local anesthetic. We investigated in vitro the antibacterial activity of tramadol in the absence of any local anesthetics against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa pathogens that can cause infectious complications after local or regional anesthesia. METHODS: Bacterial cultures were grown for 18 h, diluted in sterile physiological saline, and incubated for 6 or 24 h at 37 degrees C with 6.25, 12.5, or 25 mg/mL tramadol. The mixtures were then plated onto blood agar and colony counts were recorded after 24 h incubation at 37 degrees C. RESULTS: Tramadol had bactericidal activity against E. coli and S. epidermidis compared with controls: at 25 mg/mL for 6 h or at 12.5 mg/mL for 24 h, tramadol decreased by approximately 7 log(10) (P < 0.001) the colony counts of E. coli (100% kill). Similar results were obtained with S. epidermidis, with approximately 6 log(10) reduction (100% kill) when tramadol was used at 25 mg/mL for 24 h (P < 0.001). The antibacterial effect of 25 mg/mL tramadol was lower against S. aureus and P. aeruginosa, reducing the growth of these strains by approximately 3log(10) after 24 h (P < 0.001). CONCLUSIONS: Tramadol has dose- and time-dependent bactericidal activity against E. coli and S. epidermidis, as well as antibacterial activity against S. aureus and P. aeruginosa. The antibacterial properties of tramadol may be useful for reducing the risk of bacterial infection after local or regional anesthesia.

Sufentanil modifies the antibacterial activity of bupivacaine and ropivacaine.

PURPOSE: The purpose of our study was to investigate the effect on the growth of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Enterococcus faecalis (E. faecalis) of bupivacaine at a final concentration of 0.77 mg.mL(-1), ropivacaine at 1.2 mg.mL(-1), and sufentanil at 0.38 and 0.5 microg.mL(-1) (alone or in combination with bupivacaine and ropivacaine). METHODS: The strains were diluted to approximately 3 x 10(4) cfu.mL(-1) in Mueller-Hinton broth. The anesthetics (0.5 mL) were incubated with the bacterial suspensions (0.5 mL) for 24 hr at 37 degrees C. RESULTS: Bupivacaine inhibited the growth of E. coli (59 +/- 0.8%; P < 0.05) and S. aureus (22 +/- 3.6%; P < 0.05). Ropivacaine also inhibited the growth of E. coli (41 +/- 1.2%; P < 0.05) and S. aureus (25.5 +/- 4.1%; P < 0.05). Both anesthetics were ineffective against E. faecalis. Sufentanil only inhibited S. aureus (13.8 +/- 3.1%; P < 0.05) at a concentration of 0.5 microg.mL(-1). Sufentanil modified the antibacterial activity of bupivacaine and ropivacaine. It increased the inhibitory effect of bupivacaine on E. faecalis and S. aureus by 10 +/- 2.1% (P < 0.05) and on E. coli by 7% (P < 0.05). Sufentanil did not increase the inhibitory effect of ropivacaine on the growth of S. aureus. On the other hand, sufentanil reduced the inhibitory effect of ropivacaine on E. coli by 11% (P < 0.05). CONCLUSION: Both bupivacaine and ropivacaine alone or combined with sufentanil inhibited the growth of E. coli and S. aureus. E. faecalis was partially sensitive to a bupivacaine + sufentanil mixture. Sufentanil had a partial synergistic effect on bupivacaine and a partial antagonistic effect on ropivacaine's antibacterial activity.