Effect of chlorhexidine on genital microflora, Neisseria gonorrhoeae, and Trichomonas vaginalis in vitro

BACKGROUND: Chlorhexidine is a disinfectant that has been used in skin and mouth washes and as a preservative in some vaginal lubricants. A gel containing 0.25% chlorhexidine gluconate has been found to be effective against Chlamydia trachomatis in vitro and in animal models. Applied vaginally, 5 g of this gel could achieve vaginal fluid concentrations of < or = 1250 microg/ml. GOAL: To test the in vitro activity of chlorhexidine in a gel over a pH range of 4 to 8 in the presence or absence of blood. STUDY DESIGN: Organisms were exposed to chlorhexidine for 30 minutes to 2 hours, and the minimum cidal concentration (MCC) was calculated. RESULTS: The MCC for Neisseria gonorrhoeae was 25 microg/ml at 30 minutes and 12.5 microg/ml at 1 to 2 hours of exposure, whereas the MCC for Trichomonas vaginalis was 1250 microg/ml. Chlorhexidine was more active at pH 8 than pH 4, and less active in the presence of blood. The MCC for Lactobacillus crispatus was 1250 microg/ml at pH 4 and only 125 microg/ml at pH 8. CONCLUSIONS: Based on its in vitro activity, chlorhexidine may be an appropriate topical microbicide for prevention of gonorrhea, but not for prevention of trichomoniasis. This study suggests that the presence of blood and pH affect the activity of chlorhexidine against genital pathogens and commensals.