Activity against anaerobic organisms includes the bacteroides species and fusobacterium, gram-positive cocci, clostridium, peptostreptococcus, and peptococcus. Metronidazole has bactericidal, amebicidal, and trichomonacidal properties. Metronidazole is widely distributed into most tissues and fluids including bone, bile, pleural fluid, peritoneal fluid, CSF, and cerebral and hepatic abscesses.
Distribution is similar when the dose is given intravenously or via the oral route.
Studies have evaluated extending the dosing interval of metronidazole. Surgical patients received prophylactic 500mg IV metronidazole q12h to evaluate the appropriateness of twice daily dosing. Metronidazole trough concentrations achieved with this extended dosing interval were above the MIC for anaerobic bacteria and peak concentrations were far in excess of that required for optimal activity. More recently, Freeman, et al, evaluated single daily dosing of metronidazole. Two clinical B. fragilis isolates were used to test the bactericidal activity of the antibiotic regimen.