Infections of an endodontic nature that are associated with orofacial pain are typically caused by obligate anaerobic bacteria. Given the spectrum of action, penicillins are the preferred antibiotic of choice. Drugs in this class act against the obligate anaerobes but, also affects the substrate interrelationships amongst various bacterial strains within the infection. As some of the strains of bacteria start to die, the others are unable to survive. The penicillins include amoxicillin as well as Augmentin (an amoxicillin and clavulanate combination).
When penicillin is not effective, clindamycin may be used as it acts against anaerobic bacteria. However, clinician’s should use this antibiotic with caution as it has the potential to cause pseudomembranous colitis.
Metronidazole can also be considered alone or in combination with penicillin or amoxicillin. This drug targets gram-negative obligate anaerobes.
Source: Dental Secrets, Elsevier, 2015