FLAGYL (metronidazole) tablets, 250 mg or 500 mg is an oral formulation of the synthetic nitroimidazole antimicrobial What is the use of Flagyl 200mg 400mg 500mg? - Flagyl has been used successfully in: septicaemia, bacteraemia, brain abscess, necrotising pneumonia, osteomyelitis, puerperal sepsis, pelvic abscess, pelvic cellulitis