81. Antiseptics and disinfectants

From greek.doctor

A disinfectant is a compound which destroys or inhibits the growth of microorganisms on non-living objects, like tables, walls, beds, etc.

An antiseptic is a compound which destroys or inhibits the growth of microorganisms on living tissue, like on the skin or on mucous membranes. They are not meant for systemic use, which separates them from antibiotics.

An ideal antiseptic (or disinfectant) must have the following properties. It must:

  • destroy or remove all pathogenic microorganisms
  • act at relatively low concentrations
  • not destroy or harm the skin, mucous membranes or non-living materials
  • not be systemically toxic for humans after absorption
  • not have a strong odour
  • be stable against air and light
  • not stain objects and tissues
  • be cheap
  • be biologically degradable
  • not be inactivated by organic material like blood, pus, etc.

Asepsis

Asepsis is the state of being free from pathogenic microorganisms. Being aseptic is important in surgical fields to prevent infections. The term is also used to refer to those measures which are used to induce asepsis.

Sterilization

Sterilization is a technique which completely destroys or removes all microbial life, including spores and prions, from the surface of an object or in a fluid. There are many methods of sterilization, like heating, steaming, radiating and filtration, but the most important for us is the use of chemicals for sterilization.

Phenol coefficient

The phenol coefficient of an antiseptic (or disinfectant) is a measure of how high its bactericidal activity is. The efficacy of the antiseptic is compared to that of phenol. It’s measured as which concentration of the antiseptic must be applied to have the same bactericidal effects as phenol. For example, if a you need 0,1 mol/L of a new antiseptic to have the same antiseptic effects as 1 mol/L phenol the phenol coefficient of the new antiseptic will be 10.

Alcohols

Compounds

  • Isopropanol
  • Ethanol

The compounds are used in relatively high concentrations, 60-70%.

Mechanism of action

Alcohols denaturate proteins and dissolves lipids.

Antimicrobial spectrum

Bacteria, enveloped viruses, fungi. Not spores or parasites.

Uses

Alcohols can be to disinfect skin and mucous membranes and as disinfectants. They’re often used in combination with other antiseptics or disinfectants.

Ethanol dries out skin, but isopropanol doesn’t. Alcohols are inactivated by biological material, so they can’t disinfect surfaces which are stained by biological material.

Glycols

Compound

Triethylene glycol.

Mechanism of action

Same as for alcohols (?).

Use

Aerosolized triethylene glycol is used to sterilize air.

Aldehydes

Compounds

  • Glutaraldehyde
  • Formaldehyde

Mechanism of action

Aldehydes react with amino moieties of proteins, precipitating them.

Antimicrobial spectrum

Bacteria, viruses, fungi and spores. Aldehydes have the widest antimicrobial spectrum.

Use

Aldehydes damage tissues, so they can’t be used as antiseptics. Glutaraldehyde is used to sterilize surfaces and equipment. Formaldehyde gas is used to sterilize rooms.

Aldehydes are allergenic. Formaldehyde vapour is carcinogenic and an irritant.

Phenol and phenol derivatives

Compounds

  • Phenol
  • Phenol derivatives
    • Cresols
    • Hexachlorophene

Phenol itself was the first antiseptic agent which was used. It’s toxic if it reaches the system, it is irritating, and it is corrosive. For those reason, phenol itself is not used as an antiseptic.

Hexachlorophene itself was also previously used as a disinfectant and in cosmetics, but it was found to be neurotoxic.

Mechanism of action

Same as for alcohols (?).

Antimicrobial spectrum

Cresols are bactericidal and parasiticidal. Hexachlorophenes is mostly only active against Gram-positive bacteria.

Uses

Disinfection of equipment and surfaces. Amylmetacresol, a type of cresol, is the active ingredient in Strepsils.

Phenol can be used to treat ingrown toenails.

Biguanides

Compounds

Chlorhexidine is the only important biguanide. It is often dyed yellow.

Mechanism of action

Chlorhexidine binds to and disrupts cell walls, causing leak of intracellular components.

Antimicrobial spectrum

Bacteriostatic. Not effective against pseudomonas.

Use

Chlorhexidine is used for disinfection of the skin and mucous membranes. Chlorhexidine can also be used as a mouthwash. However, it discolours teeth.

Chlorhexidine is often combined with alcohols. It can also be used as a preservative.

Chlorine and chlorine compounds

Compounds

  • Chlorine
  • Chlorine compounds
    • Sodium hypochlorite

Sodium hypochlorite is the main ingredient of household bleach.

Mechanism of action

Oxidization and denaturation of DNA, RNA, proteins.

Antimicrobial spectrum

Bacteria, viruses, fungi, spores. The antimicrobial activity of chlorine and chlorine compounds is pH dependant, but they are active at physiological pH.

Use

Hypochlorite can be used to disinfect equipment and surfaces.

Chlorine is used to sterilize water.

Iodine and iodine compounds

Iodophors are combinations of iodine and a solubilizing agent.

Compounds

  • Lugol’s iodine
  • Iodophors
    • Povidone-iodine

Lugol’s iodine is a mix of iodine, potassium iodine and water.

Mechanism of action

Iodophors halogenate and damage DNA, RNA and proteins.

Antimicrobial spectrum

Bacteria, fungi, viruses, spores.

Use

Antisepsis of skin and mucous membranes. Preoperative antisepsis of skin. Lugol’s iodine is also used during Gram staining.

Oxidizing agents

Compounds

  • Hydrogen peroxide
  • Benzoyl peroxide
  • Ozone
  • Peracetic acid

Mechanism of action

Catalase reacts with the peroxides, releasing free radicals which damage lipids, proteins, DNA, RNA.

Antimicrobial spectrum

Bacteria, viruses, fungi, spores.

Use

Hydrogen peroxide has many uses. It can be used as an antiseptic and a disinfectant. In low concentrations it can be used to clean contact lenses. It can also be used as a bleaching agent.

Hydrogen peroxide is inactivated by organic material, so it can’t disinfect surfaces which are stained by biological material. It’s also corrosive.

Benzoyl peroxide is often used in anti-acne creams (Basiron®), as it kills Propionibacterium acnes.

Ozone is used to sterilize air or water.

Peracetic acid is used to sterilize equipment.

Heavy metals

Compounds

  • Inorganic mercury
  • Organic mercuries
    • Thiomersal
  • Silver
  • Zinc oxide

Mechanism of action

Heavy metals are biocidal thanks to the so-called oligodynamic effect. Heavy metals, even in very low concentrations, bind to sulphur and nitrogen atoms in proteins. This precipitates proteins.

Antimicrobial spectrum

Bacteria.

Uses

Mercury itself is toxic and not used. Thiomersal is an excellent preservative for vaccines, as it allows the use of more than one dose in each vial. However, the anti-vaccination movement has forced health authorities to stop using thiomersal in vaccines in North America and Europe, despite there not being any evidence that it is harmful. Thiomersal is still used in vaccines in other parts of the world.

Silver can be used as adjuvants in vaccines and antibiotics, increasing their efficacy. It can also be used to coat materials which should be antibacterial.

Zinc oxide is often used in deodorants and sunscreen.

Quaternary ammonium compounds

Quaternary ammonium compounds are cationic detergents, as opposed to regular detergents, which are anionic.

Mechanism of action

These compounds increase the permeability of plasma membranes and denaturate proteins. The quaternary nitrogen mediates these effects.

Detergents reduce surface tension.

Antimicrobial spectrum

Gram-positive bacteria and fungi.

Use

By reducing the surface tension these compounds can increase the effect of other disinfectants and antiseptics. They’re often combined with chlorhexidine. They can be used alone to clean equipment and surfaces.

Cationic detergents are inactivated by soaps (which are anionic detergents) and organic material.

Urinary antiseptics

Unlike normal antiseptics, urinary antiseptics are given systemically, but they only exert antiseptic activity when meeting with urine.

Compounds

  • Methenamine (Hiprex®)
  • Mandelic acid
  • Nalidixic acid

Mechanism of action

Methenamine releases formaldehyde when in acidic environment, like the urine.

Use

Methenamine can be used to prevent urinary tract infections but cannot be used to treat the infections themselves.

Mandelic acid and nalidixic acid are no longer used as they are toxic.