Drug of choice to treat ANUG (acute necrotizing ulcerative gingivitis) is:

• A. Metronidazole
• B. Pen VK
• C. Amoxicillin
• D. Tetracycline

Answer: (A)

ANUG is driven by anaerobic bacteria, including spirochetes and fusiform bacteria, that thrive in the gingival crevice. The antibiotic chosen should effectively target these anaerobes and reach the periodontal tissues where the infection resides. Metronidazole fits this need because it has strong activity against obligate anaerobes and spirochetes while sparing many aerobes, helping to disrupt the problematic organisms without overwhelmingly disturbing the rest of the oral flora. It also penetrates gingival crevicular fluid well, leading to better therapeutic levels where the infection is located. This makes it the most reliable option for ANUG. Penicillin VK and amoxicillin have broader activity that includes some aerobes and are less focused on anaerobes, so they’re not as consistently effective against the dominant organisms in ANUG. Tetracycline can cover anaerobes and spirochetes but carries more concerns about side effects and contraindications, which limits its use as the first choice.