Differences in antimicrobial activity of four commercial 0.12% chlorhexidine mouthrinse formulations:: an in vitro contact test and salivary bacterial counts study

Aim: To evaluate the in vitro and in vivo antimicrobial activity of four commercial 0.12% chlorhexidine mouthrinses. Material and methods: The in vitro antimicrobial activity test consisted in a modified contact test where 20 selected bacterial species were tested during 1 min with each test product. After the contact, the inoculum was cultured, and the results were expressed in terms of survival/resistance and the percentage of survival as compared to a saline control. The in vivo test consisted of a double-blind, randomized, crossover salivary bacterial counts study. 10 volunteers rinsed during 1 min with each tested product. Saliva samples were obtained before rinsing, and after 5 min, and 1, 3, 5 and 7 h. These samples were cultured both aerobically and anaerobically. Percentages of survival, in regard to baseline, were calculated for each time point. Comparisons among products were tested using anova and selected paired t-test. Results: The in vitro contact test showed no survival in any tested species with CHX+CPC, while three species (Lactobacillus casei, Streptococcus mitis and Peptostreptococcus micros ) were resistant to the other three products. CHX and CHX+NaF demonstrated additional resistant species (three and four species, respectively). The in vivo salivary bacterial counts test showed higher reductions of CHX+CPC and CHX+ALC in aerobic and anaerobic bacteria, lasting for 5 h. Significant differences were detected at multiple time points, when these two products were compared both with the control and the other tested products. Conclusion: Important differences in activity, among 0.12% CHX products, were detected by both in vitro and in vivo tests. The formulation with alcohol was more active than those without alcohol, excepting the formulation with CHX+CPC, in which the reformulation and addition of CPC not only compensate but rather increase the antimicrobial activity.