Which antibiotic is considered first-line for anaerobic odontogenic infections in penicillin-allergic patients?

• A. Amoxicillin
• B. Doxycycline
• C. Clindamycin
• D. Cephalexin

Answer: (C)

When treating anaerobic odontogenic infections in someone with a penicillin allergy, clindamycin is the best choice because it has strong activity against the anaerobic bacteria that commonly drive these dental infections and it penetrates bone and infected tissues well. Odontogenic infections are often polymicrobial, with anaerobes such as Peptostreptococcus, Bacteroides (including some oral anaerobes), and Fusobacterium playing major roles. In the setting of penicillin allergy, beta-lactam antibiotics are avoided, so an agent with reliable anaerobic coverage becomes essential. Clindamycin effectively targets these organisms and also covers many oral streptococci, providing broad enough coverage for typical dental infections while allowing good tissue penetration to the site of infection. The other options either have limited anaerobic activity (which is vital here), or rely on penicillin-like mechanisms that aren’t suitable for someone with a penicillin allergy, or have less reliable activity against the usual anaerobes involved. Keep in mind clindamycin carries a risk of Clostridioides difficile–associated diarrhea, which is a consideration in all patients.