Daniel A. Klein

Inactivation of chlorhexidine gluconate on skin by incompatible alcohol hand sanitizing gels

Incompatibility of leave-on products with an antimicrobial residual can negate the efficacy benefits of chlorhexidine gluconate (CHG) persistence. Two marketed alcohol products containing Carbomer were tested using a pigskin substrate model against Staphylococcus aureus. The CHG residual achieved a 4.22 log(10) reduction (standard deviation [SD] = 0.32) in this study, which was dramatically reduced to a 0.54 (SD = 0.50) and 0.46 (SD = 0.56) after subsequent treatment with incompatible alcohol gel products. A marketed alcohol product containing a nonionic thickener maintained the efficacy of the CHG chemical reservoir (log(10) reduction = 4.26, SD = 0.00). Similar findings were demonstrated when alcohol solutions containing the individual thickening agents were tested as simple formulations. An in vivo test using human forearms and Serratia marcescens similarly demonstrated that the activity of a CHG reservoir (log(10) reduction = 3.73, SD = 0.86) was not reduced by a nonionic thickened product (log(10) reduction = 3.98, SD = 0.72) but was significantly reduced by treatment with alcohol products containing anionic thickeners carbomer (log(10) reduction = -0.32, SD = 0.34) or acrylates/C10-30 alkyl acrylate crosspolymer (log(10) reduction = -0.20, SD = 0.32). The use of anionic thickeners or emulsifiers in leave-on products, including alcohol hand sanitizers, may inactivate the persistent antibacterial activity of CHG.

Clinical correlation of a skin antisepsis model

The use of pigskin as a test substrate for evaluating topical antimicrobial activity has been developed. Simulated handwashing protocols with this in vitro model in parallel with in vivo studies have been evaluated, based on an ASTM method for the clinical evaluation of a healthcare personnel handwash. Using Serratia marcescens as the test organism, similar log reductions were observed using the in vitro model when compared to in vivo efficacy. Results suggest that this model can be used as a reliable indicator of antiseptic efficacy on the skin. The use of sterilized skin simplifies the use of this model for both efficacy and skin-pathogen interaction studies.