Antimicrobial and
astringent agents
Antimicrobial
agents: These are the chemicals or its preparation that help
in reducing or preventing infection due to microbes. There are several terms
used in describing anti-microbial activity. First let’s study the definition of
these terms.
Antiseptic: These
are the agents or substances that are able to kill or prevent the growth of
microorganisms that is fungi, bacteria, etc. They widely applied on the living
tissues. They act by inhibiting the growth of microbial multiplication and
metabolic activities or by killing the microorganisms. An ideal antiseptic
kills the microorganism without causing any damage to the host. They can be
applied to all parts of the body and used in the form of mouthwashes, soaps,
deodorants, nasal spray, etc.
Disinfectants: These
are the agents or substance that prevents infection by the destruction of
pathogenic microorganisms. They are usually applied to the non-living things
like for the sterlisation of surgical equipment. It is helpful in maintaining
the public places like sanitation or even in hospital etc. Some chemical
disinfectants are too irritant and corrosive to the skin or tissue, so it not
used on the living tissue.
Germicide: These
are substances that kill the microbes. This is further used more specifically
for different types of microbes like, bactericide for bacteria, fungicide for
fungus, virucide for virus, etc.
Those agents which do not kill the microbes but just inhibit
the growth of microorganisms are described by terms using the suffix stat for
examples like bacteriostat, fungistat, etc., as the Greek word static's means
'standing still'.
The term's antiseptic and germicide may be further specified
according to their area and type of use as topically or internally. Internal
agents are those absorbed systemic and that not absorbed internally that is
nonsystematic.
An antimicrobial agent should have the following properties.
1. It should posse antiseptic or germicide activity and not
bacteriostatic activity.
2. It should have rapid onset of action and sustained
activity.
3. It should show good activity whatever might be the
concentration of agent used.
4. It should not cause local cellular damage or should not
interfere with body defenses.
5. It should not show any systemic toxicity from topical
application.
6. It should have broad spectrum of activity against
bacteria, fungi, protozoa, etc.
7. The topical antimicrobial agent should have favorable
lipid water distribution coefficient so that its effectiveness has been best.
Mechanism
of action:
The Mechanism of action of these agents may range from mild
astringent to powerful oxidative processes. Inorganic compounds are generally
not used internally but for topical application like oral, skin infection, etc.
Inorganic compounds generally exhibit antimicrobial action
by involving either of the following three mechanism through,
1. Oxidation. 2. Halogenation. 3. Protein binding or
precipitation.
These represent the primary chemical interactions or
reactions that occur between microbial protein and agent and result in death or
inhibition of growth of microbes.
Oxidation
mechanism: Compounds acting by this mechanism belong to class of
peroxide peroxyacids, oxygen liberating compounds like permanganate and certain
oxo halogen anions. These anti-infective agents bring about oxidation of active
functional groups present in proteins or enzymes, which are necessary for the
growth, or survival of microorganisms and also which reducing in nature. These
cause a change in the shape of the protein and there by alter its function.
For examples: A free sulfhydryl group has been essential for
function of various proteins and enzymes. If this free sulfhydryl group is
destroyed by oxidation into formation of di sulfide group, the microorganism
will die because of the altered protein molecule.
Halogenation
mechanism: Compounds that are able to liberate the chlorine or
hypochlorite or iodine act by this mechanism. The category of agents act on the
peptide linkage and alter its potential and property. The destruction of
specific function of protein causes death of microorganisms.
Most of the enzymes are proteineous in nature. A protein
molecule is composed of a variety of amino acids connected through a peptide
linkage (-CONH-) if an hypo chlorites attaches the peptide linkage by replacing
the H by Cl then protein molecule will have an altered structure and the
microorganisms.
Amino acid-CONH- Amino acid halogenation
Amino acid -COCl-Amino acid.
(Protein structure) (Altered
structure)
Protein
precipitation: This type of
mechanism involves the interaction of protein with metallic ions having large
charge or radius ratio or strong electrostatic fields. Hence most of the metals
belonging to groups IB, IIB, IIIA or transition metals show protective activity
but alkali alkaline earth metals do not show this activity. The nature of
interaction of metal with protein takes place through polar group of protein,
which acts as ligand and metal ions as Lewis acid. The chelate formed may be
strong chelate giving rise to inactivation of protein. This action in general
non-specific and at sufficient concentration will react with host as well as
with microbial protein. The protein precipitant properties of metal cations can
be altered accordingly to the concentration at the site of action.
By increasing the concentration, antimicrobial, astringent,
irritant and corrosive properties are available.
The various inorganic compounds studied under above
mechanism are as follows:
Potassium permanganate, Boric acid, Hydrogen peroxide*,
Chlorinated lime*, Iodine and its preparations
Hydrogen
peroxide
Chemical formula:
H2O2
Molecular weight:
34.0 g/mol
Standards:
Hydrogen Peroxide Solution (20 Vol) contains not less than 5.0 per cent w/v and
not more than 7.0 per cent w/v of H2O2, corresponding to about 20 times its
volume of available oxygen.
Method of
Preparation:
1. It is obtained adding thick paste of barium or sodium
peroxide in ice cold water to a calculated quantity of ice cold solution of
sulphuric acid. The insoluble barium sulphate
Chemical reactions:
Na2O2 + H2SO4 → H2O2
+ Na2SO4
2. By electrolysis of 50 percent ice cold sulphuric acid.
First per disulphuric acid will be formed which on distillation under reduced
pressure gives hydrogen per oxide. The yield of hydrogen peroxide is 30%. The
distillate containing hydrogen per oxide is analysed and is adjusted to the
required strength.
Chemical reactions:
2H2SO4 → H2S2O8
H2S2O8 + 2H2O → 2H2SO4
+ H2O2
Description:
• A clear, colourless liquid; odourless
• It decomposes in contact with oxidisable organic matter
and with certain metals and also if allowed to become alkaline
Assay
Principle: REDOX TITRATION PERMANGANOMETRIC TITRATION.
The assay method is based on the oxidation-reduction that is
redox titration; the assay is based on the reducing property of the hydrogen
per oxide. Simultaneous oxidation and reduction takes place between hydrogen
peroxide and potassium permangate, in presence of the acidic media, which is
maintained by sulphuric acid, the hydrogen per oxide is oxisidised to oxygen
and permanganate ion is reduced to manganese ion. In this titration potassium
permanganate acts as self-indicator, the end point is appearance of permanent
pale pink
Chemical
reactions:
2KMnO4 + 3 H2SO4 +
5H2O2 → K2SO4 + MnSO4 + 5O2 + 8H2O
Storage: Store protected from light in containers resistant
to hydrogen peroxide at a temperature not exceeding 30°C. If the solution does
not contain a stabilising agent, it should be stored in a refrigerator (2° to
8°C). It should not be stored for long periods
Medicinal
uses:
• Anti-microbial
agent
• Bleaching agent
• Antidote for
phosphorus and cyanide poisoning
Iodine
Chemical formula:
I2
Molecular weight:
253.8 g/mol
Standards: Iodine
contains not less than 99.5 per cent and not more than 100.5 per cent of Iodine
Method of
Preparation:
Iodine is obtained by natural source, by extracting kelp
(seaweed’s ash) with water. The solution is concentrated to remove salts of
sulphate and chloride leaving freely soluble sodium and potassium iodide in the
mother liquor. To this solution sulphuric acid is added to remove sulphur and
sulphides, which gets liberated, from small amount of thio sulphates and
sulphide is allowed to settle down. The mother liquor is decanted and to this
solution manganese di oxide is added and iodine distils over
Chemical reactions:
2NaI + 3H2SO4 + MnO→
MnSO4 + 2NaHSO4 + I2 + 2H2O Description:
• Heavy,
bluish-black, rhombic prism or plates having metallic lusture
• Peculiar odour
• Irritant
• It volatilises
at ordinary temperature
• Freely soluble
in chloroform and ether, soluble in water in presence of potassium iodide
Storage: Store in
ground-glass-stoppered containers or in earthenware containers with waxed
bungs.
Medicinal uses:
• Counter irritant
• Disinfectant
• Proper thyroid
functioning
Preparations of
Iodine
• Aqueous iodine
solution
• Weak iodine
solution
• Strong iodine
solution
• Povidone-Iodine
solution
Aqueous
iodine solution
Synonym: Lugols
solution
Standards: It is
having 5%w/v of iodine and 10 % w/v of potassium iodide in purified water
Composition:
• Iodine --- 50g
• Potassium iodide
--- 100g
• Purified water
sufficient to produce-----1000 ml
Method of
preparation: Potassium iodide and iodine are first of dissolved in 100 ml
of water with trituration or shaking process. Then the volume is made upto 1000
ml with purified water.
Description
• Transparent
• Brown liquid,
• Having the smell
of iodine
Storage condition:
It is preserved in well closed container of glass or plastic which are
resistant to iodine. It is not stored in metallic containers because iodine
attacks metal.
Medicinal uses:
• Good source of
iodine (internally)
• Externally as
germicide, fungicide
Advantages:
• Non irritant
Weak iodine
solution
Synonym: Iodine
tincture or tincture of iodine
Standards: It
is having 2%w/v of iodine and 2.5 % w/v of potassium iodide in 50 % alcohol
Composition:
• Iodine --- 20g
• Potassium iodide
--- 25g
• Alcohol (50%) to
produce-----1000 ml
Method of
Preparation: Potassium iodide and iodine are first of dissolved in
100 ml of 50 % alcohol. Then the volume is made upto 1000 ml with 50 % alcohol
Description:
• Transparent
• Brown liquid,
• Having the smell
of iodine
Storage condition: It is preserved in well closed container
of glass or plastic which are resistant to iodine. It is not stored in metallic
containers because iodine attacks metal.
Medicinal
uses:
• Good source of
iodine (internally)
• Externally as
germicide, fungicide
• Well known
antiseptic
Disadvantages:
• Irritant
Strong
iodine solution
Standards: It
is having 10 %w/v of iodine and 6 % w/v of potassium iodide in 90 % alcohol
Composition:
• Iodine --- 100g
• Potassium iodide
--- 60g
• Purified water
sufficient----100 ml
• Alcohol (90%) to
produce-----1000 ml
Method of
Preparation: Potassium iodide and iodine are first of dissolved in
100 ml purified water. Then the volume is made upto 1000 ml with 90 % alcohol
Description:
• Transparent
• Brown liquid,
• Having the smell
of iodine
Storage
condition: It is preserved in well closed container of glass or
plastic which are resistant to iodine. It is not stored in metallic containers
because iodine attacks metal.
Medicinal
uses:
• Good source of
iodine (internally)
• Externally as
germicide, fungicide
• Well known
antiseptic
Disadvantages:
• Irritant
Povidone
–Iodine solution
It is an aqueous solution of Povidone iodine. It is complex
produced by the interaction between iodine and Povidone (Poly vinyl
pyrrolidine). The complex is having about 10 % of iodine.
Description:
• Yellowish brown,
amorphous powder,
• Having a
characteristic odour
• Soluble in water
and alcohol
• The solution is
transparent in nature and has reddish brown colour and faint smell of iodine
• Its aqueous
solution is having acidic pH
Storage: It
is kept in a closed container and remains stable. Medicinal uses:
• Bactericidal
• Disinfection of
skin cuts and wounds and even applied on burnt cases also.
Advantages:
• Water
solubility
• Nonirritant
• Less toxicity
• Non staining in
nature
Potassium
permanganate
Chemical
formula: KMnO4
Molecular
weight: 158.0g/mol
Standards: Potassium
Permanganate contains not less than 99.0 per cent and not more than 100.5 per
cent of KMnO4
Method of
Preparation: On large scale potassium permanganate is prepared by
mixing a solution of potassium hydroxide with manganese di oxide and potassium
chlorate. The mixture is boiled, evaporated to yield the residue which is
heated in iron pans until it has acquired a paste consistency.
Chemical reactions:
3MnO2 + KOH + KClO3
→K2MnO4 + 3H2O+ KCl
Potassium manganate (green) so formed is extracted with
boiling water and a current of chlorine or carbon di oxide or ozonised air is
passed in to the liquid until it gets converted to permanganate. The manganese
di oxide so formed is removed continuously so as to prevent its breaking down
to manganate.
Chemical reactions:
6K2MnO4 + 3Cl2 → 6
KMnO4 + 6KCl
The solution of potassium permanganate is drawn off from any
precipitate of manganese di oxide which is then concentrated and crystallised.
The crystals are then centrifuged and dried.
Description:
• A dark purple or
brownish black, granular powder or dark purple or almost black slender,
prismatic crystals
• Having a
metallic lustre
• Odourless.
• It decomposes on
contact with certain organic substances
Storage: Store
protected from moisture
Medicinal
uses:
• Anti-microbial
agent
• Antiseptic in
mouth wash
• Anti-dote:
Barbiturates, chloral hydrate
• Veterinary practice:
antiseptic
Chlorinated
lime
Chemical
formula: Ca(OCl) Cl
Molecular
weight: 142.9 8g/mol
Standards: It
contains not less than 30 per cent w/w of chlorine
Synonym: Calcium
hypochlorite, Calcium oxychloride, Bleaching powder
Method of
preparation: By action of chlorine gas on calcium hydroxide. Calcium
hydroxide is spread on the shelves in a suitable container, then the chlorine
gas is introduced at the top of the chamber and then allowed to pass through
the contents of the shelves. This step is carried out at 25oC, thereby
minimising the formation of calcium chloride, when absorption of chlorine gas
gets completed, powdered lime is blown into the chamber to absorb the excess of
calcium chlorate.
Chemical
reaction:
Ca (OH)2 +
Cl2 → Ca(OCl) Cl + H2O
Description
It occurs as a dull white powder having a charteristic
odour. When exposed to air, gradually absorbs moisture and gradually gets
decomposed. Slightly soluble in water and alcohol
Assay: Principle:
Based on Redox titration, Iodometric titration
The available chlorine in the compound is liberated by the
action of acetic acid, then an equivalent weight of chlorine gas is replaced
with iodine by the action of potassium iodide. The liberated iodine is then
titrated against sodium thio sulphate using starch as mucilage. Until the blue
colour changes to colourless
Chemical
reactions:
Ca (OCl)Cl
+ 2CH3COOH →(CH3COOO)2Ca + Cl2 + H2O Cl2+ 2KI→ I2+ 2KCl
I2+
2Na2S2O3 → 2NaI + Na2S4O6
Storage: Store
in well closed container in a cool place
Medicinal
Uses:
• Disinfectant
• Bleaching agent
Boric acid
Chemical
formula: H3BO3
Molecular
weight: 61.8
Standards: Boric
Acid contains not less than 99.5 per cent and not more than 100.5 per cent of
H3BO3, calculated on the dried basis
Synonyms: Borarcic
acid, ortho boric acid
Method of
preparation: Boric acid may be prepared by reacting borax (sodium
tetra borate deca hydrate) with a mineral acid, such as Sulphuric acid
Na2B4O7 +H2SO4 + 5H2O
→ Na2SO4 + 4H3BO3
Description:
• A white,
crystalline powder or colourless shiny plates unctuous to the touch or white
crystals
• Odourless
• Slightly acidic
and bitter in taste
• Stable in air
• Weak acid
pKa=9.19
Storage:
Store protected from moisture
Medicinal
uses:
• Anti-microbial
agent: weak germicide
• Local
anti-infective
• Aqueous solution: eye wash and mouth
wash
• Dusting powder
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