Chlorhexidine Nanoemulsion: A New Antiseptic Formulation

Nanoparticle solutions have been studied to improve antimicrobial effect. The aim of this study was to develop, characterize, and evaluate the in vitro and in vivo antiseptic efficacy of 0.25% aqueous-based chlorhexidine nanoemulsion (NM-Cl 0.25% w/v).

The NM-Cl 0.25% w/v (2.5mg/mL) and free chlorhexidine nanoemulsion (FCN; same composition of NM-Cl without the molecule of chlorhexidine) were synthetized by the spontaneous emulsification method. Characterization analyses of physical and chemical properties were performed. The NM-Cl 0.25% w/v was compared with chlorhexidine 0.5% alcohol base (CS-Cl 0.5%) in vitro studies (microdilution study and kill curve study), and in vivo study (antisepsis of rats dorsum). Kruskal-Wallis test was used between groups and inside the same group, at different sample times and the Mann-Whitney test was performed when difference was detected.

The NM-Cl 0.25% w/v presented adequate physicochemical characteristics for a nanoemulsion, revealing a more basic pH than FCN and difference between zeta potential of NM-Cl 0.25% w/v and FCN. The NM-Cl 0.25% w/v and CS-Cl 0.5% solutions were more effective on Gram-positive than on Gram-negative bacteria (p≤0.05). NM-Cl 0.25% w/v presented upper antiseptic effect in the microdilution study and residual antiseptic effect was maintained for a longer time when compared to CS-Cl 0.5% (kill curve study). The four-fold (minimal inhibitory concentration) of NM-Cl 0.25% were the formulations with most durable effect within those tested, presenting residual effect until T6 for both bacteria. In the in vivo study, both formulations (NM-Cl 0.25% w/v and CS-Cl 0.5%) had a reduction of the microorganisms in the skin of the rats (p<0.0001) not revealing any difference between the formulations at different times, showing the antiseptic effect of NM-Cl (p≤0.05).

Both in vitro and in vivo experiments demonstrated that NM-Cl showed promising future as an antiseptic for cutaneous microbiota.