The Antibacterial Activity of Tramadol Against Bacteria Associated with Infectious Complications After Local or Regional Anesthesia

Abstract

In Brief 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°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°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 log10 (P < 0.001) the colony counts of E. coli (100% kill). Similar results were obtained with S. epidermidis, with approximately 6 log10 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 3log10 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. IMPLICATIONS: Tramadol has dose- and time-dependent bactericidal activity against Escherichia coli and Staphylococcus epidermidis as well as antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa. The antibacterial properties of tramadol may be useful for reducing the risk of bacterial infection after local or regional anesthesia.