Just add water? Chlorhexidine's antimicrobial properties are minimally affected by dilution in saline compared to...

Dilute chlorhexidine gluconate (CHG) in sterile water is an antiseptic solution approved for intraoperative wound irrigation by the United States Food and Drug Administration. In practice, however, CHG is commonly diluted with normal saline, which can result in its precipitation potentially reducing the antimicrobial effect. The purpose of this study was to determine if the antimicrobial properties of CHG are reduced after dilution with normal saline compared to sterile water.

Sterile paper disks were placed into undiluted 4% CHG (positive control), 0.05% CHG in sterile water, 0.05% CHG in normal saline, or normal saline alone (negative control) and then placed in triplicate onto the agar plates inoculated with Staphylococcus aureus. After incubating at 37 °C for 24 h, the diameter of the zone of inhibition around each disk was measured.

The mean zone of inhibition for 4% CHG, 0.05% CHG in sterile water, 0.05% CHG in normal saline, and normal saline alone was 24 ± 0.6 mm, 16 ± 0.9 mm, 14 ± 0.5 mm, and 0 ± 0 mm, respectively (p < 0.01). The zone of inhibition for dilute CHG in normal saline was on average 2.5 mm less (95% CI 1.7-3.2 mm) than that of CHG in sterile water.

Dilute CHG in normal saline, versus sterile water, retained its antimicrobial activity with a small reduction in the zone of inhibition. Surgeons and scientists should be aware of the interaction between normal saline and CHG. Future scientific studies need to control for what solution is used for dilution.