Efficacy of two iso-propanol-based skin antiseptics applied to human skin with many sebaceous glands for 2 and 10 minutes

Background: Recent research suggests that specific ethanol-based skin antiseptics exhibit their efficacy on the resident skin flora of the forehead in only 2.5 minutes. We have now looked at the efficacy of two skin antiseptics based on 63% (w/w) propan-2-ol (iso-propanol) and applied for 10 and 2 minutes on skin with a high density of sebaceous glands. Methods: Each experiment was performed in a reference-controlled cross-over design with at least 20 participants. Application of isopropanol (70%, v/v) for 10 minutes to the forehead served as the reference treatment. Pre-values and post-values (immediately after the application and after 30 min) were obtained by swabbing a marked area of 5 cm(2) for about 10 s. Swabs were vortexed in tryptic soy broth containing valid neutralizing agents. After serial dilution aliquots were spread on tryptic soy agar. Colonies were counted after incubation of plates at 36°C for 48 h. The mean log(10) reduction of bacteria was calculated. The Wilcoxon matched-pairs signed-ranks test was used for a comparison of treatments. Results: Skin antiseptic A applied for 10 min (one experiment) was equally effective to the reference treatment. When applied for 2 min (two experiments) it was still equally effective to the reference treatment immediately after application (e.g. 1.6 versus 1.4 log(10) reduction) and after 30 min (1.7 versus 1.4 log(10) reduction). Skin antiseptic B applied for 10 and 2 min (one experiment each) was also equally effective to the reference treatment both immediately after application and after 30 min. Conclusions: The clear and coloured skin antiseptics applied for 2 min on the skin of the forehead fulfilled the national efficacy requirements for skin antisepsis. The shorter application time on skin with a high density of sebaceous glands will allow acting more efficiently in clinical practice.