Ropivacaine 0.1% with sufentanil 1 μg/mL inhibits in vitro growth of Pseudomonas aeruginosa and does not promote multiplication of Staphylococcus aureus

We investigated the effect of ropivacaine combined with sufentanil, a mixture frequently used for postoperative epidural analgesia, on the growth of Staphylococcus aureus and Pseudomonas aeruginosa at room temperature. Aliquots of suspension of S. aureus and P. aeruginosa in saline were transferred into test tubes containing either a mixture of ropivacaine 0.1% and sufentanil 1 μg/mL (R+S) or saline (SA), with the latter serving as control. At 0, 3, 6, 24, and 48 h after inoculation, 1 mL of each solution was spread over standard blood agar. The plates were incubated at 22°C for 48 h, and the numbers of colony-forming units (cfu) were counted. The growth ratio for both bacterial strains was calculated as cfu time (t n )/cfu baseline (t 0 ). The primary efficacy variable was the area under the curve (AUC) in (cfu t n /cfu t 0 ) × time, based on the growth ratios. The AUC for P. aeruginosa was significantly less in R+S than in SA (P = 0.028). Multiplication of P. aeruginosa (growth ratio >1) was observed for at least 6 h after inoculation in SA. Growth of P. aeruginosa was significantly less in R+S than in SA at 3 h (P = 0.043) and 24 h (P = 0.012) after inoculation. The AUC for S. aureus did not differ significantly between R+S and SA (P = 0.74). Neither R+S nor SA promoted multiplication of S. aureus. Forty-eight hours after inoculation, growth of S. aureus was significantly less in R+S than in SA (P < 0.0001). We conclude that R+S inhibited growth of P. aeruginosa and did not promote multiplication of S. aureus when compared with SA.