Alcohols for Use as an Antimicrobial Agent

March 4, 2021


In healthcare and pharmaceutical settings, alcohol refers to two water-soluble chemical compounds, ethyl alcohol and isopropyl alcohol, that can be used as antimicrobial agents. Isopropyl alcohol is widely used as a sanitizing agent in pharmaceutical companies. It is used to avoid the risk of cross-contamination by microorganisms. Alcohols have also been used as hard surface (nonskin) disinfectants, including low-level disinfectants in health care settings as far back as the late 1800s.1

Alcohol: A Proven Disinfectant and Anti-Bacterial

Alcohols possess many features desirable for a disinfectant or antiseptic. They have excellent bactericidal efficacy as well as bacteriostatic action as a preservative, some virucidal efficacy (especially against enveloped viruses), and fungicidal efficacy.

The low-molecular-weight alcohols evaporate readily and are therefore, under regular use conditions, not considered a risk for acquired microbial resistance (as compared to actives claiming persistent effect), are relatively inexpensive, are usually easily obtainable, are colorless but can be easily colored if needed, and are relatively nontoxic with topical (skin) application. Many alcohols can also have a surface cleaning action due to their lipid solvency and low surface tension.2

However, alcohol does not contain typical ingredients found in a one-step cleaner disinfectant, including surfactants, sequestrants, and chelating agents. The presence of organic soil can reduce the effectiveness of the alcohol as a sanitizing agent. It is important when using alcohol that the surface is clean and free from organic soils.

Alcohols have been commonly used as hard-surface disinfectants because of their general antimicrobial properties. However, volatility and flammability can be an issue when using alcohols in this manner. The flash points of ethanol and propanol are below 15°C, requiring caution in their use.

Mechanisms of Action

Most chemical germicides act at multiple sites of the cell. It is believed that alcohols generally behave the same way. The primary mode of action is related to coagulation/denaturation of proteins and solubility of the alcohols in lipids.

Without water, coagulation cannot occur, therefore a 70% solution of isopropyl alcohol or ethanol will be more effective than higher concentrations of alcohol. Higher concentrations of alcohol may deprive the bacteria cell of water, thereby inducing an impermeable cell membrane. Biocidal activity drops sharply when diluted below 50% alcohol concentration, and the optimum bactericidal concentration is 60%–90% solutions in water (volume/volume).3 Low molecular weight alcohols possess less surface tension than water and thus have better wetting characteristics. Wetting characteristics are important to achieve contact time for kill of microorganisms.

The general mechanisms of alcohols can be summarized as follows:

  • Coagulation/denaturation of proteins and lipids
  • Water-dependent activity due to water requirement to achieve cell membrane permeability
  • Cytoplasmic components coagulate after intracellular concentration
  • Disruption of cell membrane followed by cell lysis4

Alcohols are known for their effectiveness against a wide variety of bacteria and viruses at concentrations of 70%-95%. Alcohols have little killing effect when it comes to spores.

Ethyl alcohol, at concentrations of 60%–80%, is a potent viricidal agent inactivating all the lipophilic viruses (e.g., herpes, vaccinia, and influenza virus) and many hydrophilic viruses (e.g., adenovirus, enterovirus, rhinovirus, and rotaviruses, but not hepatitis A virus (HAV) or poliovirus).

Isopropyl alcohol is not active against the nonlipid enteroviruses, but is fully active against the lipid viruses. Studies also have demonstrated the ability of ethyl and isopropyl alcohol to inactivate the hepatitis B virus(HBV) and the herpes virus, and ethyl alcohol to inactivate human immunodeficiency virus (HIV), rotavirus, echovirus, and astrovirus.5

What types of regulations are on alcohol use in cleaning applications?

In the United States the regulation of alcohols depends mostly on the product application. Skin antiseptics fall under the US Food and Drug Administration (FDA) and are regulated as drugs, either as an over-the-counter drug under a drug monograph guideline, or as a new drug approval, whereas alcohol-based antimicrobials for inanimate surface applications are regulated by the US Environmental Protection Agency.6

Typically, alcohols in the United States do not have efficacy claims on the label, therefore testing is required by the end-user to determine required contact time for specific efficacy. Historically, a 10-minute contact time on hard surfaces has been effective, however a 10-minute contact time is often difficult to achieve in a cleanroom environment where air changes are high and alcohol evaporates quickly.

While the FDA leaves testing up to the end-user for efficacy of alcohols, in Europe, the EU Biocidal Products Regulation (BPR) concerns the marketing, sale, and use of biocidal products that are intended to protect humans, animals, materials, or articles against harmful organisms like pests or bacteria, due to the action of the active substances contained in the biocidal product. This regulation aims to improve the functioning of the biocidal products market in the EU, while ensuring a high level of protection for humans and the environment.

The main requirement of BPR regulation is that all biocidal products require an authorization by the European Chemicals Agency (ECHA) before they can be placed on the EU market, and the active substances contained in that biocidal product must be previously approved; this includes alcohols. Information in the BPR authorization can be useful in determining contact times when employing alcohols in a controlled environment.

Alcohols are widely used in controlled environments throughout the world. Alcohols are suitable and effective for some applications, but not all. Because alcohols do not kill spores, it is not recommended for sporicidal usage. Care must be taken when determining use for alcohols in any controlled environment due to contact time and flammability considerations. Alcohols Have many useful and practical properties, and are widely used for hand sanitization of gloves, sanitization of surfaces, and removal of disinfectant residues.