Metronidazole.

Metronidazole, a nitroimidazole derivative, is a unique antimicrobial agent that is active against both bacterial and parasitic organisms, although only the anaerobic members of these groups are susceptible. It has been used for the treatment of trichomoniasis for almost 30 years and is also effective in amebiasis and giardiasis. More recently, metronidazole has emerged as a principal agent for the treatment of anaerobic infections. It is highly effective against all species of anaerobes except certain non-spore-forming gram-positive bacilli and cocci and is the only agent rapidly bactericidal against the Bacteroides fragilis group. The hydroxy metabolite is 65% as effective as metronidazole and may play a major therapeutic role. Clinical studies have substantiated its efficacy for prophylaxis during elective colorectal surgical procedures and the treatment of deep abdominal sepsis (usually in combination with another agent such as an aminoglycoside). Metronidazole is the treatment of choice for bacterial vaginosis and seems to be as effective as vancomycin for treatment of Clostridium difficile-related diarrhea and colitis. Good blood levels are produced after both oral and intravenous administration, and side effects are infrequent and minimal. Metronidazole should not be taken during the first trimester of pregnancy because of concerns about mutagenicity. Tinidazole and ornidazole are recently developed nitroimidazole derivatives that have even greater antimicrobial activity than metronidazole.