|ATC code||D08, D09 (dressing), R02|
|Appearance||100% is white or yellow powder; gelatinous lumps; Solutions BC50 (50%) & BC80 (80%) are colorless to pale yellow solutions|
|Solubility in water||very soluble|
|EU classification||C, N |
|R-phrases||R21/22, R34, R50 |
|S-phrases||S36/37/39, S45, S61 |
|Flash point||250 °C (if solvent based)|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Benzalkonium chloride, also known as BZK, alkyldimethylbenzylammonium chloride and ADBAC, is a cationic surface-acting agent belonging to the quaternary ammonium group. It has three main categories of use: as a biocide, a cationic surfactant, and phase transfer agent in the chemical industry. The chemical is a nitrogenous mixture of alkylbenzyldimethylammonium chlorides of various even-numbered alkyl chain lengths.
Benzalkonium chloride is readily soluble in ethanol and acetone. Although dissolution in water is slow, aqueous solutions are easier to handle and are preferred. Solutions should be neutral to slightly alkaline, with colour ranging from colourless to a pale yellow. Solutions foam profusely when shaken, have a bitter taste and a faint almond-like odour which is only detectable in concentrated solutions.
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.
The applications of benzalkonium chloride are extremely wide ranging, from disinfectant formulations, such as being an active ingredient in Dettol and Lysol brand products, to microbial corrosion inhibition in the oilfield sector, and a multi-surface mould, algae and moss remover.
It is used in:
- Skin antiseptics, such as Bactine, to protect scrapes and cuts
- Pharmaceuticals such as throat lozenges & various leave-on skin antiseptics
- Hand sanitizers
- Preservative in pharmaceuticals and personal care products such as eye, ear and nasal drops, as a preservative
- Hygienic towelettes and wet wipes
- Cleaners for floor and hard surfaces as a disinfectant
- Soak solutions for surgical/dental instruments prior to high-level sterilisation
- Spray disinfectants for hard surface sanitisation
- Over-the-counter single-application treatments for herpes, cold-sores, and fever blisters, such as RELEEV and Viroxyn
- Algaecide for clearing of algae, moss, lichens from paths, roof tiles, swimming pools, masonry and in horticultural greenhouse disinfection
Hand sanitizers based on benzalkonium chloride are more effective due to better residual activity and less irritant than alcohol gels. As an antiseptic, it has the advantage of not burning when put on a wound, which is not the case with ethanol-based antiseptics or hydrogen peroxide.
The greatest biocidal activity is associated with the C12 dodecyl & C14 myristyl alkyl derivatives. The mechanism of bactericidal/microbicidal action is thought to be due to disruption of intermolecular interactions. This can cause dissociation of cellular membrane lipid bilayers, which compromises cellular permeability controls and induces leakage of cellular contents. Other biomolecular complexes within the bacterial cell can also undergo dissociation. Enzymes, which finely control a wide range of respiratory and metabolic cellular activities, are particularly susceptible to deactivation. Critical intermolecular interactions and tertiary structures in such highly specific biochemical systems can be readily disrupted by cationic surfactants.
Benzalkonium chloride solutions are fast-acting biocidal agents with a moderately long duration of action. They are active against bacteria and some viruses, fungi, and protozoa. Bacterial spores are considered to be resistant. Solutions are bacteriostatic or bactericidal according to their concentration. Gram-positive bacteria are generally more susceptible than Gram-negative. Activity is not greatly affected by pH, but increases substantially at higher temperatures and prolonged exposure times. In a 1998 study utilizing the FDA protocol, a non-alcohol sanitizer utilizing the active ingredient benzalkonium chloride met the FDA performance standards, while Purell, a popular alcohol-based sanitizer, did not. The study found that a benzalkonium chloride-based sanitizer was the most favorable non-alcohol-based hand sanitizer. Advancements in the quality and efficacy of benzalkonium chloride in current non-alcohol hand sanitizers has addressed the CDC concerns regarding gram negative bacteria, with the leading products being equal if not more effective against gram negative, particularly New Delhi metallo-beta-lactamase 1 and other antibiotic resistant bacteria.
Newer formulations using benzalkonium blended with various quaternary ammonium derivatives can be used to extend the biocidal spectrum and enhance the efficacy of benzalkonium based disinfection products. Formulation techniques have been used to great effect in enhancing the virucidal activity of quaternary ammonium-based disinfectants such as Virucide 100 to typical healthcare infection hazards such as hepatitis and HIV. The use of appropriate excipients can also greatly enhance the spectrum, performance and detergency, and prevent deactivation under use conditions. Formulation can also help minimise deactivation of benzalkonium solutions in the presence of organic and inorganic contamination.
Effectively formulated quaternary ammonium disinfectants are effective at very low ppm levels, and are now the disinfectants of choice for hospitals. This is on account of user and patient safety on contact with treated surfaces and the absence of harmful fumes. Benzalkonium solutions for hospital use tend to be neutral to alkaline, non-corrosive on metal surfaces, non-staining, and safe to use on all washable surfaces. Solutions are incompatible with soaps, and must not be mixed with anionic surfactants. Hard water salts can also reduce biocidal activity. As with any disinfectant, it is recommended that surfaces are free from visible dirt and interfering materials for maximal disinfection performance by quaternary ammonium products.
Benzalkonium chloride is highly toxic to fish (LC50 = 280 μg ai/L), very highly toxic to aquatic invertebrates (LC50 = 5.9 μg ai/L), moderately toxic to birds (LD50 = 136 mg/kg-bw), and slightly toxic to mammals (LD50 = 430 mg/kg-bw). Benzalkonium chloride formulations for consumer use are dilute solutions. Concentrated solutions (10% or more) may be toxic to humans, causing corrosivity/irritation to the skin and mucosa under prolonged contact times, and death if taken internally in sufficient volumes.
Several studies claim to have identified allergic reactions to benzalkonium chloride, although a clear distinction has not been drawn between irritation and a genuine allergic response involving immune system. Studies have been based on individuals rather than statistically significant groups  It is still widely used in eyewashes, nasal sprays, hand and face washes, mouthwashes, spermicidal creams, and in various other cleaners, sanitizers, and disinfectants.
Benzalkonium chloride is also used as a preservative in nasal pharmaceuticals. There has also been concern that long-term use of benzalkonium as a preservative in nasal sprays may cause swelling of mucosa and lead to rhinitis medicamentosa. Although some studies have found no correlation between use of benzalkonium chloride in nasal sprays and rhinitis medicamentosa, others have found benzalkonium chloride in oxymetazoline nasal spray to worsen rhinitis medicamentosa in healthy volunteers after both long-term use and short-term use. A review of the current literature by the Department of Otolaryngology–Head and Neck Surgery, University of Texas Southwestern Medical Center reveals very limited data that demonstrate statistically significant safety concerns and that the studies that raise concern are largely limited to in vitro experimental design. On the other hand, in vivo data suggest that even prolonged use of topical nasal preparations containing BKC causes no significant damage to the nasal mucosa. As a result, although continued attention should be directed toward safety issues surrounding all medication, at the present time insufficient evidence exists to justify categorical dismissal of BKC for use in aqueous nasal sprays. Instead, it is hoped that a standardized test using a more representative model for evaluating preservatives can be devised and accepted. It appears that intranasal products containing the preservative BKC are safe and well tolerated for both short- and long-term use."
Benzalkonium chloride is effective at exceptionally low concentrations; contact lens solutions typically contain exceptionally low (0.002% to 0.01%) concentrations of benzalkonium chloride for effective preservative action. K. C. Swan found that repeated use of benzalkonium chloride at 10-fold higher concentrations of 1:5000 (0.02%) or stronger can denature corneal protein and cause damage to the eye. Avoiding the use of benzalkonium chloride solutions while contact lenses are in place is discussed in the literature. 
As with antibiotics, the use of biocides at sub-inhibitory concentrations can potentially result in resistant organisms, and should be used at recommended dilutions and extended contact time to ensure effective disinfection. While resistance is rarely linked to disinfectant usage at low concentrations, a 2009 study suggested that when used in less than lethal concentrations, benzalkonium chloride solutions could result in increased resistance Pseudomonas aeruginosa, and an increase in resistance of the bacteria to the ciprofloxacin antibiotic, even though the bacterial colonies had not been previously exposed to the antibiotic.
A 2012 study reported that simultaneous ocular exposure to an inert antigen and benzalkonium chloride leads to a significant change in the systemic immune response to the administered antigen in mice, thus suggesting that the preservative's effects could be more profound than the local disruption of the epithelial barrier integrity.
- Stearalkonium chloride
- Polyaminopropyl biguanide, an alternative preservative for contact lens solutions
- Record of Quaternary ammonium compounds, benzyl-C8–18-alkyldimethyl, chlorides in the European chemical Substances Information System ESIS
- U.S. Environmental Protection Agency: Reregistration Eligibility Decision for Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC)
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- Frank T. Sanders, ed. (August 2006). Reregistration Eligibility Decision for Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC) (Report). U.S. Environmental Protection Agency Office of Prevention, Pesticides, and Toxic Substances. pp. 114. http://www.epa.gov/oppsrrd1/REDs/adbac_red.pdf. Retrieved 2009-03-31.
- Seymour Stanton Block (2001). Disinfection, sterilization, and preservation (5, illustrated ed.). Lippincott Williams & Wilkins. p. 311. ISBN 0-683-30740-1.
- Park HJ, Kang HA, Lee JY, Kim HO (2000). "Allergic contact dermatitis from benzalkonium chloride in an antifungal solution". Contact Derm. 42 (5): 306–7. PMID 10789868.
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- Mc Cay, P. H.; Ocampo-Sosa, A. A.; Fleming, G. T. A. (2009). "Effect of sub-inhibitory concentrations of benzalkonium chloride on the competitiveness of Pseudomonas aeruginosa grown in continuous culture". Microbiology 156 (Pt 1): 30–8. doi:10.1099/mic.0.029751-0. PMID 19815578.
- Galletti, J. G.; Gabelloni, M. L.; Morande, P. E.; Sabbione, F.; Vermeulen, M. E.; Trevani, A. S.; Giordano, M. N. (2012). "Benzalkonium chloride breaks down conjunctival immunological tolerance in a murine model". Mucosal Immunology. [Epub ahead of print]. doi:10.1038/mi.2012.44. PMID 22692451.
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