Primary aliphatic alcohols are germicidal. Alcohols disrupt the cell membrane or virus envelope; they also denature and coagulate proteins. In addition, alcohols lyse cells and disrupt cellular metabolism. Bactericidal activity is higher at 30°C–40°C than at 20°C–30°C. Alcohols do not destroy bacterial spores. Taken orally, concentrated alcohols are lethal.
Ethyl alcohol (ethanol) and isopropyl alcohol (isopropanol) are the most widely used alcohols. Isopropanol is slightly more potent than ethanol because of its greater depression of surface tension. These alcohols can be used in concentrations of 30%–90% in aqueous solutions; best results are usually obtained with 70% ethanol or 40%–60% isopropanol applied for at least 1 minute. In general, higher concentrations tend to be less effective; a key exception is that at least 90% ethanol is required for control of methicillin-resistant Staphylococcus aureus(MRSA). Because alcohol-based hand rinses have rapid-acting antiseptic effects, they can help minimize the transmission of transient flora acquired from infected patients and decrease nosocomial diseases.
Rubbing alcohol —also called rubbing alcohol USP (United States Pharmacopeia) orsurgical spirit BP—is a mixture of alcohols, with isopropanol as its principal ingredient. Rubbing alcohol is usually applied topically, especially after cleansing with a chlorhexidine- or iodine-based scrub, to disinfect the skin before surgery. If applied immediately after a dog or cat bite, it is very effective at preventing bacterial infection. About 70% of rubbing alcohol, which is prepared from a denatured alcohol solution, consists of pure, concentrated ethanol or isopropanol. The ethanol content generally ranges from 70% to 99%, depending on the formulation. Rubbing alcohol is colorless and can be used to disinfect instruments such as thermometers. Known instances of alcohol-based solutions becoming contaminated are rare.
Ethanol is more effective than isopropanol against calicivirus (critical in a virulent systemic feline calicivirus (FCV) outbreak, which can close down a veterinary hospital for weeks). Hand sanitizers that have ethanol or triclosan as the active ingredient have been shown to decrease the infectivity of FCV.
