Which antibiotic is the preferred treatment for anaerobic dental infections such as ANUG?

• A. Metronidazole
• B. Amoxicillin
• C. Tetracycline
• D. Azithromycin

Answer: (A)

ANUG is driven by obligate anaerobic bacteria that thrive in inflamed periodontal pockets, so the antibiotic chosen should be highly effective against anaerobes and able to reach the infected sites. Metronidazole fits this need perfectly: it is specifically active against anaerobic bacteria, penetrates well into gingival crevicular fluid and periodontal tissues, and becomes bactericidal in the absence of oxygen. Its mechanism—conversion to reactive metabolites within anaerobic cells that damage DNA—targets the very organisms responsible for ANUG, making it the most reliable option among common antibiotics for this infection.

Other antibiotics listed have broader or different spectrums of activity and don’t target oral anaerobes as effectively. Amoxicillin covers many organisms but is not as potent against anaerobes in this setting; tetracycline has broader use but carries resistance and side-effect concerns; azithromycin offers limited and less consistent anaerobic coverage in periodontal infections. Thus, metronidazole is the best fit for treating anaerobic dental infections like ANUG.