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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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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