INFLUENCE OF TOPICAL ERYTHROMYCIN PREPARATIONS FOR ACNE-VULGARIS ON SKIN SURFACE PH

Topical erythromycin is a standard regimen for inflammatory acne vulga ris because of its action against Propionibacterium acnes. Changes in P. acnes colonization are inducible by long-lasting changes of skin su rface pH. Therefore, the influence of six erythromycin preparations wi th approximative pH values of 7.5 (preparation A) to 10.2 (C) on the s kin surface pH was evaluated in healthy volunteers using a cross-over design. Following a 14-day run-in period, a constant skin surface pH ( 5.0) was found. Ten subjects received single doses 2-3 days apart; 20 volunteers applied preparations A and C for 28 days. Single doses of p reparations A and E (pH 8.0) increased skin pH to 6.99 and 8.61, respe ctively, at 15 min; it then gradually dec lined. The other preparation s induced only a minor rise of short duration. At the end of the long- term application, the skin surface pH amounted to 5.73 (A) and 5.39 (C ). There was no correlation between the effect on skin surface pH and the approximative pH of the preparations. A close relation of single-d ose and long term-effects was observed, however. The skin surface pH d uring the application of preparation A is high enough to increase P. a cnes growth about fourfold as compared with normal skin and thus may c ounteract the antibacterial effect. Clinical relevance should be evalu ated in a controlled clinical trial comparing the efficacy of preparat ion A with that of preparation C.