3. Clinical use—As an antibacterial agent, metronidazole has greatest activity against Bacteroides and Clostridium. It is the drug of choice for treatment of pseudomembranous colitis resulting from Clostridium difficile and is effective in anaerobic or mixed intra-abdominal infections and in brain abscess. Tinidazole has similar activity versus anaerobic bacteria.Metronidazole is also used for infections involving Gardnerella vaginalis and in regimens for the eradication of Helicobacter pylori in gastric ulcers. As antiprotozoal drugs, metronidazole and tinidazole are effective drugs in trichomoniasis, giardiasis, and the treatment of intestinal amebiasis and amebic hepatic abscess.