Antiseptics and disinfectants are nonselective, anti-infective agents that are applied topically.
In general, antiseptics are applied to tissues to suppress or prevent microbial infection. Disinfectants are germicidal compounds usually applied to inanimate surfaces.
Both can be covered by the more general term, biocide.
Sometimes the same compound may act as an antiseptic and a disinfectant, depending on the drug concentration
To achieve maximal efficiency, it is essential to use the proper concentration of the drug for the purpose intended.
Topical antiseptics agents are extensively used in surgery for antisepsis of the surgical site and surgeon’s hands and to disinfect surgical instruments, apparel, and hospital premises.
Spirit and betadine [iodine -povidone solution] are common antiseptics.
Most of these compounds exert their antimicrobial effect by denaturation of intracellular protein, alteration of cellular membranes (often through extraction of membrane lipids), or enzyme inhibition.
Recently, the emergence of microbial resistance to some agents, especially in the hospital environment, has led to continued research into the development of new compounds.
Antiseptics and disinfectants are extensively used in hospitals and other healthcare settings for a variety of topical and hard-surface applications.
Common antiseptics and disinfectants are discussed below.
Ethyl alcohol (ethanol, alcohol), isopropyl alcohol and n-propanol are the most widely used.
Commonly known as spirit, ethyl alcohol is a very commonly used antiseptic agent.
Alcohols exhibit rapid broad-spectrum antimicrobial activity against bacteria including mycobacteria, viruses, and fungi.
They are not able to kill the spores though known to inhibit sporulation and spore germination. Thus they are not sporicidal but sporistatic.
Due to this, they are not recommended for sterilization but are widely used for both hard-surface disinfection and skin antisepsis.
The mechanism of infection is believed to be membrane damage and rapid denaturation of proteins, with subsequent interference with metabolism and cell lysis.
Glutaraldehyde is used as a disinfectant and sterilant, in particular for low-temperature disinfection and sterilization of endoscopes and surgical equipment. Glutaraldehyde has a broad spectrum of activity against bacteria and their spores, fungi, and viruses.
Glutaraldehyde is more active at alkaline than at acidic pHs.
Low concentrations of the dialdehyde (0.1%) inhibit germination, whereas much higher concentrations (2%) are sporicidal.
Glutaraldehyde is normally used as a 2% solution to achieve a sporicidal effect
Glutaraldehyde is also a potent virucidal agent
Formaldehyde is a monoaldehyde that exists as a freely water-soluble gas. Formaldehyde solution or formalin is an aqueous solution containing 34 to 38% (wt/wt) CH2O with methanol to delay polymerization.
Its clinical use is generally as a disinfectant and sterilant in liquid or in combination with low-temperature steam. Formaldehyde is bactericidal, sporicidal, and virucidal, but it works more slowly than glutaraldehyde.
It is often used in sterilization of instruments [nonmetallic] and operation theaters.
The mechanism of action is not known.
o-Phthalaldehyde is a disinfectant with potent bactericidal and sporicidal activity and has been suggested as a replacement for glutaraldehyde in endoscope disinfection.
Chlorhexidine is probably the most widely used antiseptic products, in particular in hand washing and oral products. It is also used as a disinfectant and preservative.
Chlorhexidine is a bactericidal agent. Mycobacteria are generally highly resistant to chlorhexidine.
Chlorhexidine is not sporicidal. The antiviral activity of chlorhexidine is variable and is not considered a particularly effective antiviral agent, and its activity is restricted to the lipid-enveloped viruses. Chlorhexidine does not inactivate nonenveloped viruses such as rotavirus, HAV, or poliovirus.
Alexidine is another antiseptic that differs chemically from chlorhexidine in possessing ethylhexyl end groups. Alexidine is more rapidly bactericidal.
The diamidines are as antibacterial agents. Hexamidine, pentamidine isothionate are the examples.
Clinically, diamidines are used for the topical treatment of wounds.
The exact mechanism of action of diamidines is unknown.
Halogen Releasing Agents
Chlorine and iodine rapidly penetrate into microorganisms and attacks key groups of proteins to cause cell death.
Sodium hypochlorite, chlorine dioxide, and the N-chloro compounds such as sodium dichloroisocyanurate are examples of chlorine releasing agents.
Sodium hypochlorite solutions are widely used for hard-surface disinfection, neutralization of liquid waste disposal, disinfecting spillages of blood etc.
It is effective against human immunodeficiency virus and hepatitis B virus.
NaDCC can also be used for this purpose.
CRAs at higher concentrations are sporicidal too.
Chlorine is a hazardous substance. It is highly corrosive in concentrated solution and splashes can cause burns and damage the eyes.
Appropriate precautions must be taken.
Iodine releasing agents
Both aqueous and alcoholic (tincture) solutions of iodine are in use for more than 160 years.
Betadine is commonly used as a scrubbing agent, topical antiseptics and even for wound dressings.
They are associated with irritation and excessive staining.
Silver and its compounds have been historically used as antimicrobial agents especially for cleaning the drinking water.
Silver sulfadiazine is commonly used topically and is a combination of two antibacterial agents, Ag+, and sulfadiazine.
It has a broad spectrum of activity and produces surface and membrane blebs in susceptible bacteriae.
Hydrogen peroxide is a clear, colorless liquid that is commercially available in concentrations ranging from 3 to 90%. H2O2 is considered environment-friendly because it can rapidly degrade into the innocuous products water and oxygen.
It demonstrates broad-spectrum efficacy against viruses, bacteria, yeasts, and bacterial spores It has greater activity is seen against gram-positive than gram-negative bacteria.
H2O2 acts as an oxidant by producing hydroxyl free radicals (•OH) which attack essential cell components.
Higher concentrations of H2O2 (10 to 30%) and longer contact times are required for sporicidal activity.
The activity is significantly increased in the gaseous phase.
Peracetic acid is more potent biocide than hydrogen peroxide, being sporicidal, bactericidal, virucidal, and fungicidal at low concentrations (<0.3%)
PAA also decomposes to acetic acid and oxygen and remains active in the presence of organic loads. Its main application is as a low-temperature liquid sterilant for medical devices, flexible scopes, and hemodialyzers, but it is also used as an environmental surface sterilant.
Similar to hydrogen peroxide, peracetic acid probably denatures proteins and enzymes and increases cell wall permeability.
Phenols and Halophenoles
Phenol induces progressive leakage of intracellular constituents, including the release of K+, the first index of membrane damage
The phenolics possess antifungal and antiviral properties.
Chloroxylenol is the key halophenol used in antiseptic or disinfectant formulations. Chloroxylenol is bactericidal, but P. aeruginosa and many molds are highly resistant..
The bis-phenols are hydroxy-halogenated derivatives of two phenolic groups connected by various bridges. They exhibit broad-spectrum efficacy but have little activity against P. aeruginosa and molds. They are sporostatic against bacteriae. Triclosan and hexachlorophane are the most widely used biocides in this group, especially in antiseptic soaps and hand rinses.
It exhibits particular activity against gram-positive bacteria. Its efficacy against gram-negative bacteria and yeasts can be significantly enhanced by formulation effects.
Despite the broad-spectrum efficacy of hexachlorophene, concerns about toxicity make its use in antiseptic products limited.
Quaternary Ammonium Compounds
Quaternary ammonium compounds are sometimes known as cationic detergents. These have been used for a variety of clinical purposes such as
- Preoperative disinfection of unbroken skin
- Application to mucous membranes
- Disinfection of noncritical surfaces
Quaternary Ammonium Compounds are also excellent for hard-surface cleaning and deodorization.
These are membrane-active agents which affect gram-positive and negative bacteriae.
Quaternary ammonium compounds are sporostatic.
Quaternary ammonium compounds are not mycobactericidal but have a mycobacteriostatic action.
Examples are benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetalkonium chloride etc.
These are used as disinfectants in many heat-sensitive medical devices and surgical supplies such as cannulae, catheters, and orthopedic implants.
The most widely used active agents are ethylene oxide, formaldehyde, hydrogen peroxide and PAA
Their activity is dependent on active concentration, temperature, duration of exposure, and relative humidity
Ethylene oxide gas is mutagenic and explosive but is not harsh on sensitive equipment. Formaldehyde gas is not widely used in health care.
Vapor-phase hydrogen peroxide and PAA are considered more active but have limited penetrability and applications.
Bacterial Resistance to Antiseptics and Disinfectants
Resistance to biocides may be intrinsic or acquired. This resistance can be either a natural property of an organism. Intrinsic resistance is demonstrated by gram-negative bacteria, bacterial spores, mycobacteria, and, under certain conditions, staphylococci
Acquired resistance could be by mutation or acquisition of plasmids (self-replicating, extrachromosomal DNA) or transposons (chromosomal or plasmid integrating, transmissible DNA).
Acquired, plasmid-mediated resistance is most widely associated with mercury compounds and other metallic salts.
Viruses acquire resistance by following mechanisms
- Multiplicity reactivation
- Viral aggregation,
- Viral adaptation
McDonnell G, Russell AD. Antiseptics and Disinfectants: Activity, Action, and Resistance. Clinical Microbiology Reviews. 1999;12(1):147-179.