THE EFFECTS OF ACNE TREATMENT WITH A COMBINATION OF BENZOYL PEROXIDE AND ERYTHROMYCIN ON SKIN CARRIAGE OF ERYTHROMYCIN-RESISTANT PROPIONIBACTERIA

Concomitant application of 5% w/w benzoyl peroxide and 3% w/w erythrom ycin has previously been shown to prevent the overgrowth, on the skin of acne patients, of erythromycin-resistant coagulase-negative staphyl ococci, which occurs when the antibiotic is used alone. Two in vivo st udies were carried out to assess the ability of the same therapeutic c ombination to inhibit the growth of pre-existing erythromycin-resistan t propionibacteria and to prevent the selection of resistant strains d uring treatment. A double-blind clinical trial in 37 patients with mil d to moderate acne vulgaris showed that the combination brought about a > 3 log(10) c.f.u. reduction in total propionibacterial numbers/cm(2 ) after 6 weeks therapy (P < 0.001, Wilcoxon's matched pairs) and also significantly reduced the number of erythromycin-resistant propioniba cteria (P < 0.05). In contrast, erythromycin alone reduced the total p ropionibacterial count by < 1.5 log(10) c.f.u./cm(2) after 6 weeks (P < 0.05) and did not affect the number of erythromycin-resistant strain s. The combined formulation was significantly more effective at reduci ng total propionibacterial numbers at 6 (P < 0.01, Mann-Whitney) and 1 2 weeks (P < 0.05) than erythromycin alone, although, after 12 weeks, the anti-propionibacterial efficacy of both preparations was less mark ed. Five patients on combination therapy, and five treated with erythr omycin alone, acquired erythromycin-resistant strains de novo at week 6 or week 12. In an open study in 21 acne patients, who each carried > 10(3) c.f.u. erythromycin-resistant propionibacteria/cm(2) skin pretr eatment, the combination of erythromycin and benzoyl peroxide reduced the total propionibacterial count by > 2.5 log(10) and the number of e rythromycin-resistant strains by a similar amount (P < 0.001, Wilcoxon ). This was accompanied by highly significant reductions in acne grade and lesion counts (P < 0.001). These data suggest that the combinatio n of 5% w/w benzoyl peroxide and 3% w/w erythromycin has greater in vi vo antipropionibacterial activity than 3% w/w erythromycin alone, and brings about significant clinical improvement in acne patients with hi gh numbers of erythromycin-resistant propionibacterial strains pretrea tment.