Treatment of Impetigo

ABSTRACT & COMMENTARY

Synopsis: Most cases of impetigo in children are caused by penicillin-resistant S. aureus. Topical bacitracin is often ineffective and should not be used. Oral cephalexin and topical mupirocin are effective.

Source: Bass JW, et al. Pediatr Infect Dis 1997;16:708-710.

Bass and associates from the tripler army medical center in Honolulu, HI, have previously reported studies of the etiology and therapy of impetigo in children.1 These studies showed that S. aureus was the most common etiology and that many of these staphylococci were penicillin-resistant. In the present prospective, double-blinded study, three 10-day treatments were compared. Twenty-six children with impetigo were studied. Ten children received oral cephalexin (50 mg/d in 3 divided doses plus topical placebo). Seven children received topical 2% mupirocin ointment applied tid plus oral placebo. Nine children were treated with topical bacitracin ointment applied tid plus oral placebo.

S. aureus was cultured in all 22 patients who had lesion cultures. Of these 22 children, group A beta hemolytic Streptococcus in combination with S. aureus was cultured in three of 22 patients (14%). Ninety-five percent of the S. aureus isolates were resistant to penicillin, and 19% were resistant to erythromycin. None were resistant to cephalexin. The characteristics and size of the lesions at baseline were recorded and then evaluated for response at 3-5 and 8-10 days of treatment. There were no treatment failures in the cephalexin and mupirocin groups (0/17), while six of nine children treated with bacitracin were failures.

The authors conclude that topical bacitracin should not be used as treatment for impetigo in children. Both topical mupirocin and oral cephalexin are effective. They suggest that topical mupirocin may be more appropriate therapy for patients with only a few lesions, but that oral cephalexin may be more appropriate therapy for patients with more extensive involvement.

COMMENT BY ROBERT BALTIMORE, MD, FAAP

This was a very small study. After subtraction of patients who did not complete the full course of therapy, there were only 26 subjects. The lack of efficacy of bacitracin for treatment of impetigo has been reported before, starting with the classic study in 1962 of Burnett, who showed that orally administered erythromycin was more effective than neomycin/bacitracin applied topically.2 Since that time, numerous studies have shown the superiority of systemically administered antibiotics over topical treatment, such as neomycin, bacitracin, hexachlorophene, or a combination.1

Until the late 1980s, the systemic antibiotics of choice were the penicillins or erythromycin.4 Two developments in the late 1980s and 1990s have changed treatment considerably. One well-documented change has been the change of the bacteriology of impetigo from primarily group A Streptococcus, to now, when S. aureus predominates. As shown by this study, an antibiotic that is active against staphylococcus is usually recommended for oral treatment. The second major change in treatment of impetigo has been the introduction of mupirocin, which is a topical antimicrobial agent active against staphylococci and streptococci. A number of studies published during 1988-1990 demonstrated it to have equal efficacy to erythromycin for mild to moderately severe impetigo. Thus, the results of this study should come as no surprise, as extrapolation of previously published studies would indicate that a penicillinase-resistant oral antibiotic, such as cephalexin and topical mupirocin, would be more effective than other topicals such as bacitracin, which have been shown to be relatively ineffective.

The surprise is that topical bacitracin is still a suggested therapy for impetigo and is still used by many practitioners. No less an authority than the 1997 American Academy of Pediatrics Red Book recommends topical bacitracin treatment for "mildly affected patients."5 However, pediatric infectious diseases texts generally recommend topical mupirocin or oral penicillinase-resistant antibiotics. (Dr. Baltimore is Professor of Pediatrics and Epidemiology and Public Health, Yale University School of Medicine.)

References

    1. Dimidovich CN, et al. Am J Dis Child 1990;144:1313-15.

    2. Burnett JW. N Engl J Med 1962;266:164-169.

    3. Baltimore RS. Pediatr Infect Dis 1985;4:597-601.

    4. Peter G, (ed). 1997 Red Book: Report of the Committee on Infectious Diseases. 24th ed. Elk Grove Village, IL: American Academy of Pediatrics; 1997:478-490.