ruptured eardrum, it can lead to deafness. CHG does not meet current European specifications for a hand disinfectant. Under the test conditions of the European Standard EN 1499, no significant difference in the efficacy was found between a 4% solution of chlorhexidine digluconate and soap. In the U.S., between 2007 and 2009, Hunter Holmes McGuire Veterans Administration Medical Center conducted a cluster-randomized trial and concluded that daily bathing of patients in intensive care units with washcloths saturated with chlorhexidine gluconate reduced the risk of hospital-acquired infections. Whether prolonged exposure over many years may have carcinogenic potential is still not clear. The US Food and Drug Administration recommendation is to limit the use of a chlorhexidine gluconate mouthwash to a maximum of six months. When ingested, CHG is poorly absorbed in the gastrointestinal tract and can cause stomach irritation or nausea. If aspirated into the lungs at high enough concentration, as reported in one case, it can be fatal due to the high risk of acute respiratory distress syndrome. Mechanism of action At physiologic pH, chlorhexidine salts dissociate and release the positively charged chlorhexidine cation. The bactericidal effect is a result of the binding of this cationic molecule to negatively charged bacterial cell walls. At low concentrations of chlorhexidine, this results in a bacteriostatic effect; at high concentrations, membrane disruption results in cell death. Chemistry It is a cationic polybiguanide (bisbiguanide). It is used primarily as its salts (e.g., the dihydrochloride, diacetate, and digluconate). Deactivation Chlorhexidine is deactivated by forming insoluble salts with anionic compounds, including the anionic surfactants commonly used as detergents in toothpastes and mouthwashes, anionic thickeners such as carbomer, and anionic emulsifiers such as acrylates/C10-30 alkyl acrylate crosspolymer, among many others. For this reason, chlorhexidine mouth rinses should be used at least 30 minutes after other dental products. For best effectiveness, food, drink, smoking, and mouth rinses should be avoided for at least one hour after use. Many topical skin products, cleansers, and hand sanitizers should also be avoided to prevent deactivation when chlorhexidine (as a topical by itself or as a residue from a cleanser) is meant to remain on the skin. Synthesis The structure is based on two molecules of proguanil, linked with a hexamethylenediamine spacer. Brands Chlorhexidine topical is sold as Betasept, Biopatch, Calgon Vesta, ChloraPrep One-Step, Dyna-Hex, Hibiclens, Hibistat Towelette, Scrub Care Exidine, Spectrum-4 among others. Chlorhexidine gluconate mouthwash is sold as Dentohexin, Paroex,