Oral and Intravenous Metronidazole Concentrations in Facial Artery Musculomucosal Flap, Buccal Submucosa, and Subcutaneous Tissue—A Randomized Clinical Microdialysis Study

Effective perioperative antibiotic prophylaxis is critical in oral cavity cancer surgery. Despite metronidazole's high oral bioavailability, data on its tissue-specific distribution in reconstructive head and neck surgery remain scarce. In this randomized clinical microdialysis study, 18 patients undergoing facial artery musculomucosal (FAMM) flap reconstruction after oral cancer surgery were enrolled and randomized to receive 500 mg metronidazole twice daily, either orally (Group PO) or intravenously (Group IV). Samples were collected during the third dosing interval with microdialysis catheters placed in the FAMM flap, donor buccal submucosa, and subcutaneous neck tissue. The primary end points were the tissue-specific AUC_0-24h/MIC ratio and attainment of the treatment target (AUC_0-24h/MIC ≥ 70). The mean AUC_0-24h/MIC ratio for MIC 0.5 μg/mL ranged from 437 to 553 in Group IV and 423 to 531 in Group PO; for MIC 2 μg/mL, ratios ranged from 109 to 138 and 106 to 133 for Group IV and PO, respectively; and for MIC 4 μg/mL, ratios ranged from 55 to 69 and 53 to 66 for Group IV and PO, respectively. No statistically significant differences were observed between groups. All tissues in both groups achieved the AUC_0-24h/MIC ≥ 70 treatment target for MIC 0.5 and 2 μg/mL, but none of the tissues in any of the groups achieved the treatment target for MIC 4 μg/mL. In conclusion, both oral and intravenous metronidazole administration provided adequate tissue concentrations to reach the treatment target AUC_0-24h/MIC ≥ 70 for MIC values of 0.5 and 2 μg/mL, covering prevalent anaerobic pathogens. These findings support the clinical interchangeability of administration routes for metronidazole.