A Prospective, Observational Study Evaluating the Incidence of Metallic Taste, Compliance, and Clinical Outcomes with Metronidazole Extended-release 600 mg Compared to Immediate-release Formulations (MERIT STUDY).

BACKGROUND: Metronidazole remains a cornerstone in the management of anaerobic bacterial and protozoal infections. However, its clinical utility is often limited by adverse effects such as a metallic taste (dysgeusia), which can negatively impact treatment adherence. Extended-release (ER) formulations have been developed to optimize pharmacokinetic profiles and improve tolerability. OBJECTIVE: To evaluate the incidence of metallic taste, patient compliance, clinical outcomes, and safety of metronidazole ER 600 mg compared with immediate-release (IR) formulations. MATERIALS AND METHODS: This prospective, observational, multi-center study included 200 adult patients who were prescribed either metronidazole ER 600 mg (n = 102) or IR formulations [200/400 mg; (n = 98)]. The primary endpoint was the incidence of metallic taste. Secondary endpoints included patient-reported compliance, clinical outcomes, and safety. Assessments were conducted at baseline and on days 3 and 5. RESULTS: The incidence of metallic taste was significantly lower in the ER group compared to the IR group (8.82 vs 19.39%; p = 0.0134), representing a 54% relative risk (RR) reduction. Compliance was significantly higher in the ER group (91.18 vs 80.61%; p = 0.0241). Clinical cure rates were comparable (95.10 vs 90.82%; p = 0.2377). Both formulations were well tolerated, with only mild adverse events reported. CONCLUSION: Metronidazole ER 600 mg significantly improved tolerability and adherence while maintaining comparable efficacy and safety. It offers a clinically meaningful advantage in enhancing patient compliance for the treatment of anaerobic infections.