Antibacterial Activity of Clonidine and Neostigmine In Vitro

In Brief We conducted an in vitro study to investigate the antibacterial activity of clonidine and neostigmine on common microorganisms encountered during infectious complications after regional anesthesia. Standardized suspensions of Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli were incubated during 1, 3, 6, and 24 h at 37°C with concentrations of 37.5, 75, and 150 μg/mL of clonidine and 125, 250, and 500 μg/mL of neostigmine. After 24 h incubation at 37°C, the colony counts were compared by two-way analysis of variance. The mean colony counts for S. aureus decreased significantly from control as the exposure to clonidine increased (P < 0.05), with a ∼100% kill at 6 h for the largest concentration (150 μg/mL) and at 24 h for the intermediate concentration (75 μg/mL). Similar results were observed for S. epidermidis, with a ∼100% kill at 6 h for the largest concentrations (75 and 150 μg/mL). No bactericidal activity of clonidine was observed for E. coli and no bactericidal activity of neostigmine was observed for any of the tested strains. In the conditions of this experiment, clonidine, but not neostigmine, exhibited a concentration-dependent and time-dependent bactericidal activity in vitro on the microorganisms most frequently encountered in infectious complications after regional anesthesia. IMPLICATIONS: The results of this study show that clonidine possesses a concentration-dependent and time-dependent bactericidal activity on Staphylococcus aureus and Staphylococcus epidermidis. No bactericidal activity of clonidine was observed on Escherichia coli, and no bactericidal activity of neostigmine was observed on any tested strains.