Diluting chlorhexidine gluconate: one scrub or two?

Background: Two percent chlorhexidine gluconate (CHG) is used in preparing the skin of surgical patients. In practice, it often is diluted with saline prior to use. Whether this affects efficacy is unknown, as the manufacturer does not address dilution but does recommend scrubbing twice. We attempted to determine whether diluting CHG affects its antiseptic potency and if one scrub is as effective as two.

Methods: To test effects of CHG dilution, 60 healthy subjects were recruited and randomized into a dilution group (20%, 40%, 60%, 80%, or 100% CHG) or a control group (saline). One area of one foot of each subject was prepared, and colony-forming units (CFU) were counted at baseline and at 10 min after preparation. In a second study, 60 subjects were again recruited. Based on the previous study, a 50% dilution was applied as the scrub. Colony-forming units were calculated at baseline and after each CHG application.

Results: Baseline CFU did not differ among the dilution groups (p=0.49). Subjects in all dilution groups exhibited nearly a 100% decrease in CFU, whereas the control group exhibited an 80% decrease. These results were statistically significant (p<0.01). In the second study, the CFU values after two scrubs (mean 0.1; range 0-3) were significantly lower than after one scrub (mean 3.6, range 0-100) (p=0.02).

Conclusions: Diluting CHG to a concentration as low as 0.4% does not affect antiseptic efficacy. The manufacturer-recommended two scrubs is superior to one scrub at reducing skin bacterial colony counts.