Three is a crowd: Clinical outcomes of a twice daily versus a thrice daily metronidazole dosing strategy from a multicenter study

A comparison of clinical outcomes associated with dosing metronidazole every 8 hours versus every 12 hours: a systematic review and metaanalysis

Background

Metronidazole treats obligate anaerobic bacterial and protozoal infections, with an elimination half-life of around 8 hours. The long elimination half-life, the favorable ratio of steady-state serum levels to minimum inhibitory concentration, and the presence of active metabolites have led to the consideration of metronidazole use at 12-hour dosage intervals. This systematic review aimed to compare the clinical outcomes of twice-daily and thrice-daily metronidazole dosing.

Methods

Using the PRISMA checklist, we searched five databases to systematically identify all relevant studies published up to June 16, 2023.

Results

The final analysis included two published retrospective cohort studies of hospitalized adult patients: a single site study (n = 200) and a multisite study (n = 85) of "good" quality, as measured by the Newcastle-Ottawa scale. The reported baseline characteristics of the 8-hour and 12-hour dosing groups were comparable, and neither study identified significant differences in primary and secondary clinical outcomes. Metaanalysis of the need to escalate antibiotic therapy also showed no statistically significant differences using the Mantel-Haenszel fixed-effect method (95% confidence interval: 47.6% lower to 6.4 times higher risk, P = 0.34) and inverse-variance method (risk ratio: 1.87; 95% confidence interval: 0.52-6.65, P = 0.34).

Conclusions

This review suggests that dosing metronidazole every 12 hours is as effective as every-8-hour dosing for hospitalized patients with anaerobic infections. These encouraging findings would benefit from validation by a multicenter randomized controlled trial since there would be many benefits to a 12-hour dosing interval while achieving similar clinical outcomes with traditional dosing. The studies in this systematic review excluded patients with Clostridioides difficile and central nervous system and amebiasis infections, so the findings do not apply to these infection types.

Oral Antibiotics for Bacteremia and Infective Endocarditis: Current Evidence and Future Perspectives

Bacteremia and endocarditis are two clinical syndromes that, for decades, were managed exclusively with parenteral antimicrobials, irrespective of a given patient's clinical condition, causative pathogen, or its antibiotic susceptibility profile. This clinical approach, however, was based on low-quality data and outdated expert opinions. When a patient's condition has improved, gastrointestinal absorption is not compromised, and an oral antibiotic regimen reaching adequate serum concentrations is available, a switch to oral antibacterials can be applied. Although available evidence has reduced the timing of the oral switch in bacteremia to three days/until clinical improvement, there are only scarce data regarding less than 10-day intravenous antibiotic therapy in endocarditis. Many standard or studied oral antimicrobial dosages are smaller than the approved doses for parenteral administration, which is a risk factor for treatment failure; in addition, the gastrointestinal barrier may affect drug bioavailability, especially when the causative pathogen has a minimum inhibitory concentration that is close to the susceptibility breakpoint. A considerable number of patients infected by such near-breakpoint strains may not be potential candidates for oral step-down therapy to non-highly bioavailable antibiotics like beta-lactams; different breakpoints should be determined for this setting. This review will focus on summarizing findings about pathogen-specific tailoring of oral step-down therapy for bacteremia and endocarditis, but will also present laboratory and clinical data about antibiotics such as beta-lactams, linezolid, and fosfomycin that should be studied more in order to elucidate their role and optimal dosage in this context.