Benzalkonium chloride (BZK, BKC, BAK, BAC), also known as alkyldimethylbenzylammonium chloride (ADBAC) and by the trade name Zephiran, is a type of cationic surfactant. It is an organic salt classified as a quaternary ammonium compound. ADBACs have three main categories of use: as a biocide, a cationic surfactant, and a phase transfer agent. ADBACs are a mixture of alkylbenzyldimethylammonium chlorides, in which the alkyl group has various even-numbered alkyl chain lengths.
Solubility and physical properties
Depending on purity, benzalkonium chloride ranges from colourless to a pale yellow (impure). Benzalkonium chloride is readily soluble in ethanol and acetone. Dissolution in water is ready, upon agitation. Aqueous solutions should be neutral to slightly alkaline. Solutions foam when shaken. Concentrated solutions have a bitter taste and a faint almond-like odour.
Standard concentrates are manufactured as 50% and 80% w/w solutions, and sold under trade names such as BC50, BC80, BAC50, BAC80, etc. The 50% solution is purely aqueous, while more concentrated solutions require incorporation of rheology modifiers (alcohols, polyethylene glycols, etc.) to prevent increases in viscosity or gel formation under low temperature conditions.
Cationic surfactant
Benzalkonium chloride possesses surfactant properties, dissolving the lipid phase of the tear film and increasing drug penetration, making it a useful excipient, but at the risk of causing damage to the surface of the eye. Laundry detergents and treatments. Softeners for textiles.
Phase transfer agent
Benzalkonium chloride is a mainstay of phase-transfer catalysis, an important technology in the synthesis of organic compounds, including drugs.
Bioactive agents
Especially for its antimicrobial activity, benzalkonium chloride is an active ingredient in many consumer products: Pharmaceutical products such as eye, ear and nasal drops or sprays, as a preservative. Personal care products such as hand sanitizers, wet wipes, shampoos, soaps, deodorants and cosmetics. Skin antiseptics and wound wash sprays, such as Bactine. Throat lozenges and mouthwashes, as a biocide Spermicidal creams. Cleaners for floor and hard surfaces as a disinfectant, such as Lysol and Dettol antibacterial spray and wipes. Algaecides for clearing of algae, moss, lichens from paths, roof tiles, swimming pools, masonry, etc. Benzalkonium chloride is also used in many non-consumer processes and products, including as an active ingredient in surgical disinfection. A comprehensive list of uses includes industrial applications.
During the course of the COVID-19 pandemic, from time to time there have been shortages of hand cleaner containing ethanol or isopropanol as active ingredients. The FDA has stated that benzalkonium chloride is eligible as an alternative for use in the formulation of healthcare personnel hand rubs. However, in reference to the FDA rule, the CDC states that it does not have a recommended alternative to ethanol or isopropanol as active ingredients, and adds that "available evidence indicates benzalkonium chloride has less reliable activity against certain bacteria and viruses than either of the alcohols." In November 2020 the Journal of Hospital Infection published a study on benzalkonium chloride formulations; it was found that laboratory and commercial disinfectants with as little as 0.13% benzalkonium chloride inactivated the SARS-CoV-2 virus within 15 seconds of contact, even in the presence of a soil or hard water. This resulted in a growing consensus that BZK sanitizers are just as effective as alcohol-based sanitizers despite the CDC guidelines. As a hand sanitizer, use of BZK may be advantageous over ethanol in some situations because it has significantly more residual antibacterial action on the skin after initial application. Benzalkonium chloride has demonstrated persistent antimicrobial activity for up to four hours after contact whereas ethanol-based sanitizer demonstrate skin protection for only 10 minutes post-application.
Medicine
Benzalkonium chloride is a frequently used preservative in eye drops; typical concentrations range from 0.004% to 0.01%. Stronger concentrations can be caustic and cause irreversible damage to the corneal endothelium.
Avoiding the use of benzalkonium chloride solutions while contact lenses are in place is discussed in the literature.
Due to its antimicrobial activity when applied to skin, some topical medications for acne vulgaris have benzalkonium chloride added to increase the products’ efficiency or shelf-life.