CHAPTER 96

Antiseptics and disinfectants

Antiseptics and disinfectants are locally acting antimicrobial drugs. These agents are used to reduce acquisition and transmission of infection. Drugs suitable for antisepsis and disinfection cannot be used internally because of toxicity.

General considerations

Terminology

The terms antiseptic and disinfectant are not synonymous. In common usage, the term antiseptic is reserved for agents applied to living tissue. Disinfectants are preparations applied to objects. As a rule, agents used as disinfectants are too harsh for application to living tissue. Disinfectants are employed most frequently to decontaminate surgical instruments and to cleanse hospitals and other medical facilities. Most uses of antiseptics are prophylactic. For example, antiseptics are used to cleanse the hands of medical personnel; they are applied to the patient’s skin prior to invasive procedures (eg, surgery, insertion of needles); and they are used to bathe neonates. Rarely, antiseptics are employed to treat an existing local infection. However, in most cases, established infections are best treated with a systemic antimicrobial drug.

Several related terms may need clarification. Sterilization indicates complete destruction of all microorganisms. In contrast, sanitization implies only that contamination has been reduced to a level compatible with public health standards. A germicide is a drug that kills microorganisms. Germicides may be divided into subcategories: bactericides, virucides, fungicides, and amebicides. In contrast to a germicide, a germistatic drug is one that suppresses the growth and replication of microorganisms, but does not kill them.

Properties of an ideal antiseptic

The ideal antiseptic, like any other ideal drug, should be safe, effective, and selective. The preparation should be germicidal (rather than germistatic) and should have a broad spectrum of antimicrobial activity: The drug should kill bacteria and their spores, along with viruses, protozoa, yeasts, and fungi. Effects should have a rapid onset and long duration. Development of microbial resistance should be low. The drug should have no harmful effects on humans: It should not produce local injury, impair healing, or produce systemic toxicity following topical application. Lastly, the drug should not cause stains and should be devoid of offensive odor. No antiseptic has all of these properties.

Time course of action

Toxicity to microorganisms is determined in part by duration of exposure to an antiseptic or disinfectant. However, some agents act more quickly than others. For example, ethanol (70% solution) reduces cutaneous bacterial count by 50% in just 36 seconds. In contrast, benzalkonium chloride (at a dilution of 1:1000) requires 7 minutes to produce the same effect. Because such differences exist, effective use of antiseptics and disinfectants requires that healthcare personnel understand the exposure requirements of each agent.

Using antiseptics to treat established local infection

In the past, topical agents were used routinely to treat established local infection. Today, systemic anti-infective drugs are the treatment of choice. Why? First, systemic agents are more effective than topical drugs. Second, systemic agents don’t damage inflamed or abraded tissue. Experience has shown that antiseptics do little to reduce infection in wounds, cuts, and abrasions. This lack of efficacy is attributed to poor penetration to the site of infection, and to diminished activity in the presence of wound exudates. Although of limited value for established local infection, antiseptics are quite useful as prophylaxis: When applied properly, antiseptics can help cleanse wounds and decrease microbial contamination.

Using antiseptics and disinfectants most effectively

The principal value of antiseptics and disinfectants derives from their ability to prevent contamination of the patient by microorganisms in the environment: It appears that antiseptics applied directly to the patient contribute relatively little to prophylaxis against infection (except in patients who are neutropenic). A number of clinical studies support this conclusion. In one study, over 5000 preoperative patients were bathed with hexachlorophene. Although this treatment greatly reduced the concentration of surface bacteria, it had no effect on the incidence of postoperative infection. Similarly, in a study of patients who had undergone cardiothoracic surgery, it was found that most postoperative infections were caused by organisms not present at the site of incision. From these studies and others, we can conclude that infections are caused primarily by environmental microorganisms rather than by organisms living on the skin of the patient. Consequently, use of antiseptics by nurses, physicians, and others who contact the patient confers much greater protection than does application of antiseptics to the patient. Patients also benefit greatly by the rigorous use of disinfectants to decontaminate surgical supplies and medical buildings.

Properties of individual antiseptics and disinfectants

Antiseptics and disinfectants derive from a variety of chemical families, ranging from alcohols to iodine compounds to phenols. The various antiseptics and disinfectants differ from one another with respect to mechanism of action, time course, and antimicrobial spectrum. In almost all cases, the drugs employed as disinfectants are not used for antisepsis and vice versa. The more commonly employed antiseptics and disinfectants are listed in Table 96–1. For each drug, the table indicates chemical family and clinical use (antisepsis, disinfection, or both).

TABLE 96–1 

Antiseptics and Disinfectants: Chemical Category and Application

		Application
Chemical Category	Drug	Antisepsis	Disinfection
Alcohols	Ethanol
	Isopropanol
Aldehydes	Glutaraldehyde
	Formaldehyde
Iodine Compounds	Iodine tincture
	Iodine solution
Iodophors	Povidone-iodine
Chlorine Compounds	Oxychlorosene
	Sodium hypochlorite
Phenolic Compound	Hexachlorophene
Miscellaneous Agents	Chlorhexidine
	Hydrogen peroxide
	Benzalkonium chloride

Alcohols

Ethanol

Ethanol (ethyl alcohol) is an effective virucide and kills most common pathogenic bacteria as well. However, the drug is inactive against bacterial spores, including those of Clostridium difficile, and has erratic activity against fungi. Bactericidal effects result from precipitating bacterial proteins and dissolving membranes. Ethanol can enhance the effects of several other antimicrobial preparations (eg, chlorhexidine, benzalkonium chloride).

Ethanol is employed almost exclusively for antisepsis. The most frequent uses are hand washing by hospital staff and cleansing the skin prior to needle insertion and minor surgery. Because it has limited activity against bacterial spores and fungi, ethanol is not a good disinfectant.

Optimal bacterial kill requires that ethanol be present in the proper concentration. The drug is most effective at a concentration of 70%. Higher concentrations are less active.

Ethanol should not be applied to open wounds. Why? Because the drug can increase tissue damage and, by causing coagulation of proteins, can form a mass under which bacteria can thrive.

Ethanol for antisepsis is available in three formulations: solutions, gels, and foams. No one formulation has been proved more effective than the others.

Isopropanol

Isopropanol (isopropyl alcohol) is employed primarily as an antiseptic. When applied in concentrations greater than 70%, isopropanol is somewhat more germicidal than ethanol. Like ethanol, isopropanol can increase the effects of other antiseptics (eg, chlorhexidine). Isopropanol promotes local vasodilation and can thereby increase bleeding from needle punctures and incisions. Isopropanol is available in concentrations ranging from 70% to 100%.

Aldehydes

Glutaraldehyde

Glutaraldehyde [Cidex-7, Cidex Plus 28] is lethal to all microorganisms; the drug kills bacteria, bacterial spores, viruses, and fungi. Antimicrobial effects result from cross-linking and precipitating proteins. Glutaraldehyde is used to disinfect and sterilize surgical instruments and other medical supplies, including respiratory and anesthetic equipment, catheters, and thermometers. The drug is too harsh for antiseptic use. To completely eliminate bacterial spores, instruments and equipment must be immersed in glutaraldehyde for at least 10 hours. All blood should be removed first. Glutaraldehyde is most active at alkaline pH. However, under alkaline conditions, glutaraldehyde eventually becomes inactive owing to gradual polymerization. Consequently, alkaline solutions of glutaraldehyde are active for only 2 to 4 weeks. Glutaraldehyde should be used with adequate ventilation because fumes can irritate the respiratory tract.

Formaldehyde

Formaldehyde kills bacteria, bacterial spores, viruses, and fungi. Like glutaraldehyde, formaldehyde is too harsh for application to the skin. Accordingly, use is limited to disinfection and sterilization of equipment and instruments. For two reasons, formaldehyde is less desirable than glutaraldehyde. First, formaldehyde acts slowly: Destruction of bacterial spores may take 2 to 4 days. Second, formaldehyde is more volatile than glutaraldehyde, and hence tends to cause more respiratory irritation. As with glutaraldehyde, blood should be removed before instruments and equipment are sterilized.

Iodine compounds: iodine solution and iodine tincture

Iodine was first employed as an antiseptic more than 160 years ago. Despite the introduction of numerous other drugs, iodine remains one of our most widely used germicidal agents. The drug is extremely effective, having the ability to kill all known bacteria, fungi, protozoa, viruses, and yeasts. Additional assets are low cost and low toxicity.

The composition of iodine solution and iodine tincture is very similar. Iodine solution consists of 2% elemental iodine and 2.4% sodium iodide in water. Iodine tincture contains the same amounts of elemental iodine and sodium iodide and also contains 47% ethanol. The ethanol enhances the antimicrobial activity of iodine tincture.

The germicidal activity of iodine tincture and iodine solution is due only to free (dissolved) elemental iodine. In both the tincture and the solution, the concentration of free elemental iodine is very low—about 0.15%—owing to the poor solubility of iodine in water. Because only free iodine is active, most of the elemental iodine and all of the sodium iodide present in both iodine tincture and iodine solution do not contribute directly to microbicidal activity. However, these components do contribute indirectly by serving as reservoirs from which free elemental iodine can be released.

Iodine tincture and iodine solution are employed primarily for antisepsis of the skin, a use for which they are the most effective agents available. When the skin is intact, iodine tincture is preferred. This preparation is commonly employed to cleanse the skin prior to IV injection and withdrawal of blood for microbial culture. For treatment of wounds and abrasions, iodine solution should be employed. (Because alcohol is an irritant, iodine tincture is less appropriate for application to broken skin.)

Iodophors: povidone-iodine

An iodophor is simply a complex composed of elemental iodine plus a solubilizing agent. Antimicrobial effects derive from release of free iodine. The intact iodophor is inactive.

Povidone-iodine is an iodophor composed of elemental iodine plus povidone, an organic polymer that increases the solubility of the iodine. Povidone-iodine has no antimicrobial activity of its own. Rather, it serves as a reservoir from which elemental iodine can be released. Free elemental iodine is the active germicide. The concentration of free iodine achieved with application of povidone-iodine is lower than that produced with application of iodine tincture or iodine solution. Hence, povidone-iodine is less effective than these other iodine preparations.

Povidone-iodine is employed primarily for prophylaxis of postoperative infection. Additional uses include hand washing, surgical scrubbing, and preparing the skin prior to invasive procedures (eg, surgery, aspiration, injection). In addition, povidone-iodine is employed to sterilize equipment, although superior disinfectants are available.

The drug is supplied in a variety of formulations (ointments, solutions, aerosols, gels). It is also impregnated in swabs, sponges, and wipes. Trade names include ACU-dyne, Betadine, and Operand.

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