Antiseptics and Disinfectants

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Chapter: Essential pharmacology : Antiseptics, Disinfectants and Ectoparasiticides

The terms antiseptic and disinfectant connote an agent which inhibits or kills microbes on contact. Conventionally, agents used on living surfaces (skin, mouth) are called antiseptics while those used for inanimate objects (instruments, privies, water supply) are called disinfectants.


ANTISEPTICS AND DISINFECTANTS

 

The terms antiseptic and disinfectant connote an agent which inhibits or kills microbes on contact. Conventionally, agents used on living surfaces (skin, mouth) are called antiseptics while those used for inanimate objects (instruments, privies, water supply) are called disinfectants. There is considerable overlap and many agents are used in either way. A practical distinction between the two on the basis of a growth inhibiting versus direct lethal action is futile because these are often concentration dependent actions. The term Germicide covers both category of drugs.

 

There, however, is difference between ‘disinfection’ and ‘sterilization’. While sterilization means complete killing of all forms of microorganisms, disinfection refers to reduction in the number of viable pathogenic microbes to a level that they do not pose a risk to individuals with normal host defence. Thus, in ordinary usage, disinfectants do not eliminate all microbes.

 

The era of antiseptics and disinfectants was heralded by Semmelweiss (washing of hands in chlorinated lime) and Lister (antiseptic surgery by the use of phenol) in the 19th century. These germicides differ from systemically used antimicrobials by their low parasite selectivity—are too toxic for systemic use. However, many systemic antimicrobials are applied topically as well, and some antibiotics (bacitracin, neomycin) are restricted to topical use, but are generally not enumerated with the antiseptics.

 

A strict distinction is thus impossible.

 

A good antiseptic/disinfectant should be:

 

·            Chemically stable.

·            Cheap.

·            Non-staining with agreeable colour and odour.

·            Cidal and not merely static, destroying spores as well.

·     Active against all pathogens—bacteria, fungi, viruses, protozoa.

·            Require brief time of exposure.

·    Able to spread through organic films and enter folds and crevices.

·      Active even in the presence of blood, pus, exudates and excreta.

 

A disinfectant in addition should not corrode or rust instruments and be easily washable. An antiseptic in addition should be:

 

·          Rapid in action and exert sustained protection.

·          Nonirritating to tissues, should not delay healing.

·          Non-absorbable, produce minimum toxicity if absorbed.

·          Non-sensitizing (no allergy).

·          Compatible with soaps and other detergents.

 

Spectrum of activity of majority of antiseptic-disinfectants is wide, reflecting nonselectivity of action. However, some are rather selective, e.g. hexachlorophene, chlorhexidine, quaternary ammonium antiseptics, gentian violet and acriflavin are more active on gram-positive than gram-negative bacteria; silver nitrate is highly active against gonococci and benzoyl peroxide against P. acnes.

 

Mechanisms of action of germicides are varied, but can be grouped into:

 

·     Oxidation of bacterial protoplasm.

·     Denaturation of bacterial proteins including enzymes.

· Detergent like action increasing permeability of bacterial membrane.

 

Factors which modify the activity of germicides are:

 

·          Temperature and pH.

·          Period of contact with the microorganism.

·          Nature of microbe involved.

·          Size of innoculum.

·          Presence of blood, pus or other organic matter.

 

Potency of a germicide is generally expressed by its phenol coefficient or Rideal Walker coefficient, which is the ratio of the minimum concentration of test drug required to kill a 24 hour culture of B. typhosa in 7.5 minute at 37.5°C to that of phenol under similar conditions. This test has only limited validity, particularly in relation to antiseptics which have to be tested on living surfaces.

 

Therapeutic Index of an antiseptic is defined by comparing the concentration at which it acts on microorganisms with that which produces local irritation, tissue damage or interference with healing.

 

Classification

 

1.         Phenol derivatives: Phenol, Cresol, Hexylresorcinol, Chloroxylenol, Hexachlorophene.

 

2.         Oxidizing agents: Pot. permangnate, Hydrogen peroxide, Benzoyl   peroxide.

 

3.         Halogens: Iodine, Iodophores, Chlorine, Chlorophores.

 

4.         Biguanide:  Chlorhexidine.

 

5.         Quaternary ammonium (Cationic): Cetrimide, Benzalkonium chloride,      Dequalinium chloride.

 

6.         Soaps:  of Sod. and Pot.

 

7.         Alcohols:  Ethanol, Isopropanol.

 

8.         Aldehydes: Formaldehyde, Glutaraldehyde.

 

9.         Acids:  Boric acid, Acetic acid.

 

10.     Metallic salts: Merbromin, Silver nitrate, Silver sulfadiazine, Mild silver protein, Zinc sulfate, Calamine, Zinc oxide.

 

11.     Dyes: Gentian violet, Acriflavine, Proflavine.

 

12.     Furan derivative: Nitrofurazone.


PHENOLS

 

Phenol (Carbolic Acid)

 

It is one of the earliest used antiseptics and still the standard for comparing other germicides. It is a relatively weak agent (static at 0.2%, cidal at >1%, poor action on bacterial spores). It is a general protoplasmic poison, injuring microbes and tissue cells alike—at higher concentrations causes skin burns and is a caustic. It acts by disrupting bacterial membranes and denaturing bacterial proteins. Organic matter diminishes its action slightly while alkalies and soaps do so profoundly (carbolic soaps are not more germicidal than soap itself). It is now seldom employed as an antiseptic, but being cheap, it is used to disinfect urine, faeces, pus, sputum of patients and is sometimes included in antipruritic preparations because of its mild local anaesthetic action.

 

Cresol

 

It is methylphenol; more active (3–10 times) and less damaging to tissues. Used for disinfection of utensils, excreta and for washing hands.

 

LYSOL is a 50% soapy emulsion of cresol.

 

Hexylresorcinol

 

It is a more potent derivative of the phenolic compound resorcinol that is odourless and nonstaining; used as mouthwash, lozenge and as antifungal.

 

Chloroxylenol

 

It has a phenol coefficient of 70; does not coagulate proteins, is noncorrosive, nonirritating to intact skin, but efficacy is reduced by organic matter. It is poorly water soluble; the commercial 4.8% solution (DETTOL) is prepared in 9% terpinol and 13% alcohol; used for surgical antisepsis. A 0.8% skin cream and soap, 1.4% lubricating obstetric cream (for vaginal examination, use on forceps, etc.), and a mouthwash (DETTOLIN 1%) are also available. These preparations lose activity if diluted with water and kept for a time.

 

Hexachlorophene

 

This chlorinated phenol acts by inhibiting bacterial enzymes and (in high concentration) causing bacterial lysis. It is odourless, nonirritating and does not stain. Its activity is reduced by organic matter but not by soap. It is commonly incorporated in soap and other cleansing antiseptics for surgical scrub, patient’s skin, etc., but is narrow spectrum; kills gram-positive but not gram-negative bacteria or spores. The degerming action is slow but persistent due to deposition on the skin as a fine film that is not removed by rinsing with water.

 

Use of a 3% solution for baby bath markedly reduced the incidence of staphylococcal infections, but produced brain damage (especially in premature neonates). Around 1970 several fatalities occurred in USA. Since then use of preparations containing > 2% hexachlorophene have been banned. It is a good deodorant and is incorporated in many toilet products.

 

OXIDIZING AGENTS

 

Potassium Permanganate

 

It occurs as purple crystals, highly water soluble, liberates oxygen which oxidizes bacterial protoplasm. The available oxygen and germicidal capacity is used up if much organic matter is present—the solution gets decolourised. A 1:4000 to 1:10,000 solution (Condy’s lotion) is used for gargling, douching, irrigating cavities, urethra and wounds. The action is rather slow and higher concentrations cause burns and blistering—popularity therefore has declined.

 

It has also been used to disinfect water (wells, ponds) and for stomach wash in alkaloidal poisoning (except atropine and cocaine which are not efficiently oxidized). It promotes rusting and is not good for surgical instruments.

 

Hydrogen Peroxide

 

It liberates nacent oxygen which oxidizes necrotic matter and bacteria. A 30% solution produces 10 volumes of oxygen, much of which escapes in the molecular form. Catalase present in tissues speeds decomposition resulting in foaming—helps in loosening and removing slough, ear wax, etc. Hydrogen peroxide has poor penetrability and a weak, transient action. It loses potency on keeping. Use therefore is much restricted.

 

Benzoyl Peroxide

 

It is specifically active against P. acnes and used on acne vulgaris.

 

HALOGENS

 

Iodine

 

It is a rapidly acting, broad-spectrum (bacteria, fungi, viruses) microbicidal agent; has been in use for more than a century. Acts by iodinating and oxidizing microbial protoplasm. A 1 : 20,000 solution kills most vegetative forms within 1 min. Even bacterial spores are killed with higher concentrations/longer contact. Organic matter retards but does not abolish its germicidal action.

 

Solid iodine is corrosive, stronger solutions (> 5%) cause burning and blistering of skin. Tincture iodine (2% in alcohol) stings on abrasions. It is used on cuts, for degerming skin before surgery, and to treat ring worm, etc. Mandel’s paint (1.25% iodine dissolved with the help of Pot. iodide forming soluble I¯ions) is applied on sore 3 throat. A non-staining iodine ointment (IODEX 4%) is popular as antiseptic and counterirritant. Some individuals are sensitive to iodine—rashes and systemic manifestations occur in them.

 

Iodophores

 

These are soluble complexes of iodine with large molecular organic compounds that serve as carriers—release free iodine slowly. The most popular—Povidone (Polyvinylpyrrolidone) iodine: is nonirritating, nontoxic, nonstaining and exerts prolonged germicidal action. Treated areas can be bandaged or occluded without risk of blistering. It is used on boils, furunculosis, burns, otitis externa, ulcers, tinea, monilial/trichomonal/ nonspecific vaginitis and for surgical scrubbing, disinfection of endoscopes and instruments.

 

BETADINE 5% solution, 5% ointment, 7.5% scrub solution, 200 mg vaginal pessary; PIODIN 10% solution, 10% cream, 1% mouthwash; RANVIDONE AEROSOL 5% spray with freon propellant.

 

Chlorine

 

A highly reactive element and a rapidly acting potent germicide, 0.1–0.25 ppm kills most pathogens (but not M. tuberculosis) in 30 sec. However, the degerming action is soon exhausted, and it lacks substantivity. It is used to disinfect urban water supplies. Organic matter binds chlorine, so that excess has to be added to obtain free chlorine concentration of 0.2–0.4 ppm. This is known as the ‘chlorine demand’ of water. Chlorine is more active in acidic or neutral medium.

 

Chlorophores

 

These are compounds that slowly release hypochlorous acid (HOCl). Because of ease of handling, they are used in preference to gaseous chlorine.

 

Chlorinated lime (bleaching powder) It is obtained by the action of chlorine on lime; resulting in a mixture of calcium chloride and calcium hypochlorite. On exposure, it decomposes releasing 30–35% W/W chlorine. It is used as disinfectant for drinking water, swimming pools and sanitizer for privies, etc.

 

Sodium hypochlorite solution Contains 4–6% sodium hypochlorite. It is a powerful disinfectant used in dairies for milk cans, other equipment and for infant feeding bottles. It is unstable and too irritant to be used as antiseptic, except for root canal therapy in dentistry.

 

BIGUANIDE

 

Chlorhexidine

 

A  powerful,  nonirritating,  cationic  antiseptic  that  disrupts  bacterial   cell

membrane. A secondary action is denaturation of microbial proteins. It is relatively more active against gram-positive bacteria. Like hexachlorophene it persists on the skin. Present in SAVLON (see below), it is extensively used for surgical scrub, neonatal bath, mouthwash, obstetrics and as general skin antiseptic.

 

Chlorhexidine is the most widely employed antiseptic in dentistry. As 0.12–0.2% oral rinse or 0.5–1% toothpaste, it is highly active in preventing/treating gingivitis. Twice daily chlorhexidine oral rinse markedly reduces oral infections in immunocompromised patients, including AIDS. However, it may leave an unpleasant after taste, and repeated application causes brownish discolouration of teeth.

 

QUATERNARY AMMONIUM (CATIONIC) ANTISEPTICS

 

These are detergents; cidal to bacteria, fungi and viruses. However, many gram-negative bacteria (especially Pseudomonas), M. tuberculosis and bacterial spores are relatively resistant. They act by altering permeability of cell membranes and denaturing of bacterial proteins. Soaps, being anionic, neutralize their action, while alcohol potentiates. They spread through oil and grease, have cleansing and emulgent properties. They are nonirritating and mildly keratolytic. However, the germicidal action is rather slow and bacteria may thrive under a film formed by them on the skin. Pus, debris and porous material like cotton, polyethylene reduce their activity. Occasionally sensitization occurs. These disadvantages not withstanding, they are widely used as sanitizers, antiseptic and disinfectant for surgical instruments, gloves, etc, but should not be considered sterilizing.

 

Cetrimide

 

A soapy powder with a faint fishy odour. Used as 1–3% solution, it has good cleansing action, efficiently removing dirt, grease, tar and congealed blood from road side accident wounds. Alone or in combination with chlorhexidine, it is one of the most popular hospital antiseptic and disinfectant for surgical instruments, utensils, baths, etc.

 

CETAVLON CONCENTRATE: Cetrimide 20% SAVLON LIQUID ANTISEPTIC: Chlorhexidine gluconate 1.5% + Cetrimide 3%.

 

SAVLON/CETAVLEX CREAM: Chlorhexidine HCl 0.1% + Cetrimide 0.5%.

 

SAVLON HOSPITAL CONCENTRATE: Chlorhexidine gluconate 7.5% + Cetrimide 15%.

 

Benzalkonium chloride (Zephiran)

 

It is highly soluble in water and alcohol. A 1:1000 solution is used for sterile storage of instruments and 1 in 5000 to 1 in 10,000 for douches, irrigation, etc.

 

Dequalinium chloride Has been used in gum paints and lozenges.

 

DEQUADIN 0.25 mg lozenges.

 

SOAPS

 

Soaps are anionic detergents; weak antiseptics, affect only gram-positive bacteria. Their usefulness primarily resides in their cleansing action. Washing with soap and warm water is one of the most effective methods of preventing transmission of infection by removing/diluting pathogenic bacteria. Soaps can be medicated by other antiseptics.

 

ALCOHOLS

 

Ethanol

 

It is an effective antiseptic and cleansing agent at 40–90% concentration. The rapidity of action increases with concentration upto 70% and decreases above 90%. It acts by precipitating bacterial proteins. A cotton swab soaked in 70% ethanol rubbed on the skin kills 90% bacteria in 2 min.; has been used before hypodermic injection and on minor cuts. Low concentrations enhance the antiseptic activity of iodine and chlorhexidine when used as solvent for these. It is an irritant and should not be applied to mucous membranes or to delicate skin (scrotum), ulcers, etc. On open wounds it produces a burning sensation, injures the surface and forms a coagulum under which bacteria could grow. It is a poor disinfectant for instruments—does not kill spores and promotes rusting.

 

Isopropanol

 

It is less volatile; can be used in place of ethanol.

 

ALDEHYDES

 

Formaldehyde

 

It is a pungent gas—sometimes used for fumigation. A 37% aqueous solution called Formalin is diluted to 4% and used for hardening and preserving dead tissues. It denatures proteins and is a general protoplasmic poison, but acts slowly. A broad-spectrum germicide, but use as antiseptic is restricted by its irritating nature and pungent odour. It is occasionally employed to disinfect instruments and excreta. Those who handle formalin can develop eczematoid reactions. The urinary antiseptic methenamine acts  by releasing formaldehyde in acidic urine. Formaline is also used to precipitate toxoids from toxins.

 

Glutaraldehyde

 

It is less volatile, less pungent, less irritating and better sterilizing agent than formalin, but needs to be activated by alkalinization of the solution. It exerts broad-spectrum activity against bacteria, fungi and viruses. Organic matter does not inactivate it. A 2% solution is used to disinfect surgical instruments and endoscopes, but prolonged contact is needed. Repeated application on skin can cause sensitization. The alkalinized solution has a short shelf life (2 weeks) unless stablilizing agents are added.

 

 

ACIDS

 

Boric acid

 

It is only bacteriostatic and a very weak antiseptic. But being nonirritating even to delicate structures, saturated aqueous solutions (4%) have been used for irrigating eyes, mouthwash, douche, etc. Boro-glycerine paint (30%) is used for stomatitis and glossitis. A 10% ointment (BOROCIDE) is available for cuts and abrasion. It is included in prickly heat powders and ear drops. However, boric acid is not innocuous; systemic absorption causes vomiting, abdominal pain, diarrhoea, visual disturbances and kidney damage. Hence its use for irrigating bladder, large wounds, as ointment on extensive burnt areas, liberal use of powder for infants is not recommended.

 

Acetic acid

 

It is a relatively weak antiseptic, bactericidal only above 5%. Pseudomonas is especially susceptible. It is occasionally used for burn dressing and for douche in 1– 3% strength.

 

METALLIC SALTS

 

Mercury compounds

 

They act as bacteriostatic by inactivating SH enzymes. Though, generally considered potent, mercurials are actually poor antiseptics with low therapeutic index. Mercury is considered an environmental hazard, and use of mercurial antiseptics is not recommended.

 

Silver Compounds

 

These are astringent and caustic. They react with SH, COOH, PO4 and NH2 groups of proteins.

 

Water stored in silver vessels is said to become sterile. As the concentration of Ag+ ions is  very low, this  has  been  called  ‘Oligodynamic action’. Silver nitrate rapidly kills microbes, action persisting for long periods because of slow release of Ag+ ions from silver proteinate formed by interaction with tissue proteins. Tissues get stained black due to deposition of reduced silver. Silver nitrate touch is used for hypertrophied tonsillitis and aphthous ulcers. It is highly active against gonococci—1% solution is used for ophthalmia neonatorum.

 

Silver Sulfadiazine is highly active against Pseudomonas and has been used on burns.

 

Zinc salts

 

They are astringent and mild antiseptics.

 

Zinc sulfate: is highly water soluble, 0.1–1% is used for eyewash and in eye/ear drops (Zincboric acid drops—in ZINCOSULFA 0.1% eye drop). Applied to skin, it decreases perspiration. White lotion containing 4% each of zinc sulfate and sulfurated potash has been used for acne and impetigo; (THIOSOL 2.5%, THIOSOL FORTE 4% lotion).

 

Calamine and zinc oxide: are insoluble. In addition to being mildly antiseptic, they are popular dermal protectives and adsorbants.


DYES

 

Gentian violet (crystal violet)

 

A rosaniline dye active against staphylococci, other gram-positive bacteria and fungi, but gram-negative organisms and mycobacteria are insensitive. Aqueous or alcoholic solution (0.5–1%) is used on furunculosis, bedsores, chronic ulcers, infected eczema, thrush, Vincent’s angina, ringworm, etc. It has become unpopular due to deep staining.

 

Acriflavine and Proflavine

 

These are orange-yellow acridine dyes active against gram-positive bacteria and gonococci. Their efficacy is not reduced by organic matter and is enhanced in alkaline medium. Solutions lose efficacy on exposure to light—store in amber bottles. They are nonirritant and do not retard healing—particularly suitable for chronic ulcers and wounds. Bandage impregnated with acriflavine-vaseline is used for burn dressing;

 

ACRINOL 0.1% acriflavine cream.

 

The triple dye lotion contains gentian violet 0.25% + brilliant green 0.25% + acriflavine 0.1% (TRIPLE DY), has been used for burns and for dressing umbilical stump in neonates.

 

FURAN DERIVATIVES

 

Nitrofurazone

 

It is cidal to both gram-positive and negative, aerobic and anaerobic bacteria, even in high dilutions, but activity is reduced in the presence of serum. Acts by inhibiting enzymes necessary for carbohydrate metabolism in bacteria. It is highly efficacious in burns and for skin grafting. Its local toxicity is negligible—but sensitization occurs frequently.

 

FURACIN 0.2% cream, soluble ointment, powder. Nitrofurantoin and Furazolidone are other furan derivatives used for urinary and intestinal infections respectively.

  

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