The Diffusion of Intravenously Administered Cefuroxime and Metronidazole into the Peritoneal Fluid During Postoperative Period in Patients with Secondary Peritonitis Compared to Controls: A Pilot Study Using Peritoneal Microdialysis

Background/Objectives: To prevent surgical site infections, it is important to consider the concentration of the administered antibiotic in the target compartment. We measured the concentrations of cefuroxime and metronidazole in peritoneal fluid with the microdialysis technique in patients undergoing surgery for secondary peritonitis (7 patients) and for inflammatory bowel disease (11 patients). Methods: All patients received 1.5 g of cefuroxime and 0.5 g of metronidazole every 8 h during the postoperative period for at least 72 h. Microdialysates covering 8-h intervals were collected, and the concentration of cefuroxime and metronidazole was measured using liquid chromatography–mass spectrometry. Results: For metronidazole, a concentration of ≥4 μg/mL was reached in all but one sample, corresponding to the minimal inhibitory concentration (MIC) for most anaerobic bacteria strains. For cefuroxime, a value of ≥4 μg/mL was reached in 88% and 93% of the samples in the peritonitis group and the IBD group, respectively, corresponding to the MIC values for most Gram-negative bacteria, and a value of ≥16 μg/mL, corresponding to the MIC value for more resistant bacteria, was reached in only 40% and 23% of the samples, respectively. Conclusions: Our results show that the peritoneal microdialysis method is feasible for studying the diffusion of antibiotics into the peritoneal cavity. Measuring the accumulative concentration of antibiotics in the peritoneal fluid corresponding to the drug administration interval may provide important information to consider alongside traditional pharmacodynamic parameters and may be relevant to achieving an optimal therapeutic effect.