In-vivo Effectiveness of Adapalene 0.1%/Benzoyl Peroxide 2.5% Gel on Antibiotic-sensitive and Resistant Propionibacterium acnes.

BACKGROUND: A gel combination treatment containing a retinoid (adapalene 0.1%) and an antimicrobial (benzoyl peroxide 2.5%) has been shown to be an effective treatment for acne vulgaris, addressing three of the four pathogenic factors (hyperkeratinization, Propionibacterium acnes proliferation, inflammation) without contributing to the incidence of Propionibacterium acnes antibiotic resistance as neither the retinoid nor benzoyl peroxide creates selective pressure for resistance.
OBJECTIVE: To evaluate the effectiveness of an adapalene-benzoyl peroxide gel combination in reducing antibiotic-sensitive and resistant strains of Propionibacterium acnes on the facial skin of volunteers.
METHODS: This four-week, open-label, single-center study included 30 healthy adults with high facial Propionibacterium acnes populations [>10(4) colony-forming units per square centimeter of skin (CFU/cm(2))] and presence of subpopulations resistant to erythromycin, tetracycline, and clindamycin. The gel was applied once daily to the forehead. Cultures for total and antibiotic-resistant Propionibacterium acnes were obtained from the forehead area at screening, Baseline, Week 2, and Week 4.
RESULTS: Total Propionibacterium acnes counts decreased by 1.1 log(10) CFU/cm(2) after two weeks of treatment, and by 1.6 log10 CFU/cm(2) after four weeks. All subjects had strains resistant to each of the five antibiotics at baseline. Mean counts of erythromycin and clindamycin resistant Propionibacterium acnes were high at baseline (5.37 and 5.28 log(10) CFU/cm(2), respectively) and decreased by ≥2.1 log(10) by Week 4 (P<0.001). Mean counts of strains resistant to tetracyclines were lower at baseline (3.8 to 4.2 CFU/cm(2)) and decreased by 1.9 (tetracycline), 2.4 (minocycline), and 1.3 (doxycycline) log(10) CFU/cm(2) by Week 4 (P<0.001). LIMITATIONS: Although limited in scope, the results of the present study demonstrate that the fixed-dose combination gel containing adapalene 0.1% and benzoyl peroxide 2.5% effectively inhibited both antibiotic-susceptible and antibiotic-resistant Propionibacterium acnes. In addition to reducing population densities, therapy with adapalene-benzoyl peroxide eradicated some resistant strains entirely in some individual subjects.
CONCLUSION: Topical adapalene-benzoyl peroxide gel effectively reduced skin colonization by antibiotic-sensitive and antibiotic-resistant Propionibacterium acnes after four weeks. This trial was registered with ClinicalTrials.gov (http://clinicaltrials.gov/), registry number NCT00907101.