Author: Jeannette Y. Wick, RPh, MBA, FASCP
A new review investigates the causes of penicillin failure in treating pharyngotonsillitis as well as antibiotics that can be used in its place.
Penicillin failure is a serious concern in patients with acute and recurrent pharyngotonsillitis (PT). Although it is efficacious in vitro
, penicillin fails in vivo
in approximately 40% of cases. In these cases, it fails to eradicate Group A beta-hemolytic streptococci (GABHS), leading to persistence or recurrence of symptoms.
The causes of treatment failure may include poor penetration into the tonsillar tissues, the presence of beta-lactamase-producing bacteria, Moraxella catarrhalis
-GABHS coaggregation that enhances the GABHS colonization, or lack of competitive or interfering normal flora. When present, the normal flora produce bacteriocins (which kill other bacteria) or compete for nutrients; more than 85% of children have adequate populations of these bacteria. However, widespread penicillin use has caused a shift in the oropharyngeal flora by selecting for beta-lactamase-producing bacterial strains.
Other causes of penicillin failure include poor patient adherence and inappropriate antibiotic dose, duration, or choice. In addition, patients occasionally re-acquire their infection from a toothbrush or their braces. The goal of treatment in penicillin-resistant PT is to eradicate beta-lactamase-producing bacteria that protect GABHS from penicillin, while preserving “protective” interfering organisms.
In a review
published online on April 16, 2013, in Current Infectious Disease Reports
, Itzhak Brook, MD, of the Georgetown University School of Medicine, notes several implications of the challenge of penicillin failure for clinicians. Although penicillin is still recommended as the antibiotic of choice for GABHS PT, other antibiotics—specifically macrolides and cephalosporins for acute infection, and lincomycin, clindamycin, and amoxicillin-clavulanate for relapsing infection—eradicate bacteria and produce a clinical cure more effectively.
Cephalosporins have successfully eradicated GABHS better than penicillin; in many cases, cephalosporins have worked in 7 days, compared to the10 days required by penicillin. Cephalosporins eradicate GABHS, but preserve interfering organisms. The superiority of cephalosporins and amoxicillin-clavulanate may be due to their efficacy against GABHS and their ability to attack beta-lactamase-producing H influenzae
and M catarrhalis
Lincomycin, clindamycin, and amoxicillin-clavulanate, which are effective against aerobic and anaerobic organisms, are often superior to penicillin for recurrent PT. Evidence supporting their use in acute tonsillitis is lacking, however, and they should not be used for this condition.
Ms. Wick is a visiting professor at the University of Connecticut School of Pharmacy and a freelance writer from Virginia.