Antibiotic Overview

Penicillins

The penicillin family, including primarily penicillin V and amoxicillin, has long been the mainstay in the antibiotic treatment of odontogenic infections. Randomized controlled clinical trials comparing a penicillin with other newer antibiotics have found no statistically significant differences in clinical cure rates. (Note that the correct generic name of phenoxymethyl penicillin potassium is penicillin V. It is not penicillin VK.)

The antibacterial spectrum of penicillins includes the gram-positive cocci (except staphylococci) and oral anaerobes. Penicillin G is given parenterally, whereas penicillin V and amoxicillin are preferred for oral administration. The penicillins have little toxicity except for allergic reactions, which occur in about 3% of the population.

Amoxicillin and ampicillin are semisynthetic penicillins that are more effective against gram-negative rods compared with penicillin. Amoxicillin has the advantage of a longer serum half-life than ampicillin and penicillin, making its effective duration and its dosage interval longer. The costs of amoxicillin and penicillin are similar. Although both penicillin and amoxicillin are effective in treating odontogenic infections, amoxicillin is often preferred to penicillin because its longer dosage interval improves patient compliance. Amoxicillin is given three times per day; penicillin V and ampicillin are given four times per day.

Penicillinase-resistant penicillins such as methicillin and dicloxacillin were effective in the past for penicillinase-producing staphylococci. Since more than 85% of staphylococcus strains, especially methicillin-resistant Staphylococcus aureus , have become resistant to this class of penicillins, their usefulness has diminished.

Clindamycin

The antibacterial spectrum of clindamycin includes gram-positive cocci and almost all anaerobic bacteria. Clindamycin is effective against streptococci, some staphylococci, and anaerobes. The drug is four to five times more expensive than penicillin, and rising clindamycin resistance rates of oral streptococci are of concern. Therefore clindamycin is best used for therapeutic and prophylactic indications only in penicillin-allergic patients.

Antibiotic-associated colitis, resulting in persistent and possibly life-threatening diarrhea, has been associated with clindamycin and many other antibiotics. Its cause has been identified as the elaboration of an exotoxin by Clostridium difficile , which is resistant to clindamycin and several other antibiotics. It most typically occurs in medically debilitated patients. After diagnosis based on a stool assay for the C. difficile exotoxin, the treatment includes antibiotic therapy with oral vancomycin or metronidazole.