Benzalkonium chloride

Benzalkonium chloride (alkyl dimethyl benzyl ammonium chloride) is a mixture of alkylbenzyl dimethylammonium chlorides of various alkyl chain lengths. It is commonly used as an antiseptic and spermicide. This product is a nitrogenous cationic surface-acting agent belonging to the quaternary ammonium group. The greatest bactericidal activity is associated with the C12-C14 alkyl derivatives.

It has been considered one of the safest synthetic biocides known, and has a long history of efficacious use. However, conflicting studies cast doubt on its reputation for safety. Some products have been reformulated in light of this research, but it is still widely used in eyewashes, hand and face washes, mouthwashes, spermicidal creams, and in various other cleaners, sanitizers, and disinfectants. It is also used as an annual treatment for the elimination of bacteria in water within waterbeds. However, manufacturers of OTC artificial tears and eye washes became concerned about chemical sensitivity from long-term daily use and have in some products substituted EDTA as a preservative and have added "for sensitive eyes" to labeling. There has also been concern that long-term use of benzalkonium as a preservative in nose sprays may cause swelling of mucosa and lead to Rhinitis medicamentosa. Some manufacturers have put 3-day limits on safe use of such nose sprays.

Applications are extremely wide ranging, from disinfectant formulations to microbial corrosion inhibition in the oilfield sector. It is often used to disinfect skin prior to withdrawing blood for Blood Alcohol Content ("BAC") tests because it contains no alcohol and cannot be said to taint the BAC test.

Benzalkonium chloride is readily soluble in water, alcohol, and acetone. Formulation requires great care as Benzalkonium can be inactivated by certain organic compounds, including soap, and must not be mixed with anionic surfactants. Hard water salts can also reduce biocidal activity. Although newer formulations are more resistant to deactivation, as with any disinfectant, it is recommended that surfaces are rinsed well before disinfection.

Aqueous solutions of benzalkonium chloride are neutral to slightly alkaline, colorless, and nonstaining. Solutions foam profusely when shaken, have a bitter taste, and a faint almond-like odour, which is only detectable in concentrated solutions.

The mechanism of bactericidal/microbicidal action is thought to be due to disruption of intermolecular interactions. This can cause dissociation of cellular membrane 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 plethora 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 rapidly acting anti-infective 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.

Health concerns
Benzalkonium chloride is an allergen.