Infection prevention
The evolution of Quaternary Ammonium Compounds
In this article, Dr. Tim Sandle discusses the evolution of Quaternary Ammonium Compounds (QACs) and their application in healthcare. He provides an insight into their efficacy and sets out why the latest generation of QACs represent an advancement.
To achieve satisfactory disinfection of healthcare facilities, and to ensure pathogens are eliminated, an efficacious disinfectant is required. An ideal disinfectant should have a high inactivating capacity for a wide range of bacteria, fungi, and viruses (referred to as spectrum of activity).1
advantage of lower residue formation. Quaternary ammonium compounds are surfactants composed of positively charged polyatomic ions.2
A longstanding example is The reduction in bacterial
population is tied to the appropriateness of the disinfectant; the concentration of the agent; the method of application; and its contact time (the time that the disinfectant must remain in contact with the surface in order to reach and react with any microorganisms present). Here a balance must be drawn between a long contact time, necessary for absolute kill, and the time allotted between patient sessions. Other factors also need to be accounted for, including toxicity levels, residue formation, and personnel safety. The essential factor is, however, the efficacy of the disinfectant against the types of microorganisms that present the most significant potential patient risk. There is an array of different disinfectants available. The two groups of disinfectants that have a wide spectrum of activity and are less affected by organic soiling are quaternary ammonium compounds and amphoteric agents. Quaternary ammonium compounds have the added
benzalkonium chloride. Later generations of QACs achieve synergies through the incorporation of other chemicals designed to enhance their efficacy. This class of disinfectant has a broad-spectrum antimicrobial activity.3 The antimicrobial action of quaternary ammonium compounds involves perturbation of cytoplasm and the lipid bilayers that form the bacterial cell membrane.4 On entering the bacterial cell, the chemical forms mixed-micelle aggregates with hydrophobic membrane components; these function to solubilise membranes and cause cell lysis.5
QACs are the most widely used of the non-
oxidising disinfectants in the pharmaceutical industry and the use of these chemicals is expanding in healthcare settings, not least because of data showing good efficacy against the coronavirus agent that causes COVID-19.6 This article looks at the efficacy of quaternary ammonium compounds and compares the performance of this class of biocides with comparable disinfectants and sets out why the latest generation of QACs represent an
advancement. The article follows on from an earlier article published in The Clinical Services Journal (‘Advantages of quaternary ammonium compounds’) which considered the application of QACs as part of the infection control programme.
Quaternary ammonium compounds Quaternary ammonium compounds (QACs or sometimes “quats”) are a varied class of several hundred chemicals. QACs were first formulated and evaluated during the 1930s (beginning with Domagk’s experiments on benzalkonium chloride)7
inquiries into their antimicrobial activity go back to 1916 (based on studies by Jacobs and Heidelberg).8
QACs are defined by their
chemical structure, and this depends on the presence of four (hence ‘quaternary’) aliphatic or aromatic moieties that are attached to the central nitrogen atom (R1
R2 N+R3 R4 ). The
traditional QAC structure possesses a positively charged hydrophilic (lipophobic) moiety and a hydrophobic (lipophilic) tail. The majority of the registered QACs contain a halogen (like chloride or bromide) as anions. To meet the requirement to be classed as a QAC, the active ingredient in a disinfectant must be an organic compound that contains at least one cationic (positively charged) nitrogen atom. Two widely used types of QACs are9
:
l alkyl dimethyl benzyl ammonium chloride (ADBAC), formed of alkyl chain lengths of either C8, C10, C12, C14, C16 and C18 and,
l dodecyl didecyl dimethyl ammonium chloride (DDAC), consisting of two alkyl chains each comprising of 10 (C10) carbon atoms.
QAC disinfectants sometimes have more than one quaternary ammonium compounds in them (these are more recent ‘generations’ in QAC chemistry) or sometimes a QAC is combined with a different type of disinfectant, such as an oxidising agent. The more recent generations of QACs include
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although the earliest
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