Antimicrobial agents
Contents
• Antimicrobial agents
• The various mechanism of action of anti-microbial agents
• The monograph analysis of:
Boric acid
Hydrogen peroxide
Iodine and its preparation
Potassium permanganate
Chlorinated lime
Learning
Objectives
At the end of this
lecture, the student will be able to:
• Define antimicrobial agents
• Describe the various mechanism of action of anti-microbial
agents
• Explain the monograph analysis of:
Boric acid
Hydrogen peroxide
Iodine and its preparation
Potassium permanganate
Chlorinated lime
Antimicrobial
Agents
• kills or inhibits the growth of microorganisms such as
bacteria, fungi, or protozoans
• Antimicrobial drugs either kill microbes (microbiocidal)
or prevent the growth of microbes (microbiostatic)
Specific
terminology
• Antiseptic
• Disinfectants
• Germicides
• Bacteriostatics
• Bactericidal
• Sanitizers
An antimicrobial agent
should possess the following characteristics:
• Broad spectrum of activity
• Posses antiseptic or germicide activity
• Rapid onset and sustained activity
• Good therapeutic index
• Should not cause local cellular damage
• Should not interfere with body defence mechanism
Mechanism
of action of antimicrobial agents:
Oxidative mechanism
Halogenations mechanism
Protein precipitation mechanism
Monograph of
potassium permanganate
Name: potassium
permanganate
Chemical formula:
KMnO4
Molecular weight: 158.0
Standards:
Potassium Permanganate contains not less than 99.0 per cent and not more than
100.5 per cent of KMnO4
Method of
Preparation:
2MnO2 + 4 KOH +O2 à 2K2MnO4 + 2H2O
KOH + MnO2 + KCLO3 à KCl + K2MnO4 + 3H2O
K2MnO4 + 3Cl2 à KMnO4 + KCl
Properties of
potassium permanagante:
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
Test for purity
• Appearance of solution
• Water-insoluble matter
• Sulphates
• Chlorides
Assay:
Principle
Iodometric titration, Direct titration
2KMnO4 + 10KI + 8H2SO4 à 6K2SO4 + MnSO4 + 8H2O +
5I2
I2 + 2Na2S2O3 à 2NaI + Na2S4O6
Indicator: starch
solution
Colour change: Blue to colourless
Storage: Store
protected from moisture
Medicinal uses:
• Anti-microbial agent
• Antiseptic in mouth wash
• Anti dote:
Barbiturates, chloral hydrate
• Veterinary practice: antiseptic
Monograph of
Boric acid
Name: 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 tetraboratedecahydrate)
with a mineral acid, such as Sulphuric acid
Na2B4O7 + H2SO4 + H2O à 4H3BO3 + Na2SO4
Properties of boric
acid:
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
Test for purity
• Appearance of solution
• Heavy metals
• Solubility in ethanol
• Arsenic
• Loss on drying
• Acidity/Alkalinity
• Sulphates
Assay: Principle
Neutralization titration, Indirect titration alkali metric
Indicator:
phenolphthalein
Reagent:
Glycerine
Colour change:
colourless to pale pink
Storage: Store
protected from moisture
Medicinal uses:
• Anti-microbial agent: weak germicide
• Local anti-infective
• Aqueous solution: eye wash and mouth wash
• Dusting powder
Monograph of
Hydrogen peroxide
Name: Hydrogen
peroxide
Chemical formula:
H2O2
Molecular weight: 34.0
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. By adding barium or sodium peroxide to a solution of
sulphuric acid
Na2O2 + H2SO4 à H2O2 + Na2SO4
2. By electrolysis of 50 percent ice cold sulphuric acid
2H2SO4 à H2S2O8
H2S2O8 + 2H2O à 2H2SO4 + H2O2
Properties of
hydrogen peroxide:
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
Test for purity
• Organic stabilizers
• Non-volatile matter
• Acidity/Alkalinity
Assay: Principle
Redox Permanganometry titration
2 KMnO4 + 3 H2SO4 + 5H2O2 à K2SO4 + MnSO4 + 5O2 + 8H2O
Indicator:
potassium permanganate
Media: sulphuric
acid
Colour change:
colorless to permanent pink
Storage: Store
protected from light in containers resistant to hydrogen peroxide at a
temperature not exceeding 30°. If the solution does not contain a stabilising
agent, it should be stored in a refrigerator (2° to 8°). It should not be
stored for long periods
Medicinal uses:
• Anti-microbial agent
• Bleaching agent
• Anti-dote for phosphorus and cyanide poisoning
Monograph of
Iodine
Name: Iodine
Chemical formula:
I2
Molecular weight:
253.8
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)
• Concentrated – to remove salts of sulphate and chloride
• Add sulphuric acid: removes sulphur and sulphides
• Mother liquor is decanted
• To this solution manganese di oxide is added
• Iodine distils over
2NaI + 3H2SO4 + MnO2 à MnSO4 + 2NaHSO4 + I2 +
2H2O
Properties of Iodine:
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
Test for purity
• Chlorides and bromides
• Cyanogen
• Nonvolatile matter
Assay: Redox
titration
I2 + 2Na2S2O3 à 2NaI + Na2S4O6
Indicator: Starch
Colour change:
blue -colourless
Formulations of
Iodine
• Aqueous iodine solution
• Weak iodine solution
• Strong iodine solution
• Povidone-Iodine solution
Storage: Store in
ground-glass-stoppered containers or in earthenware containers with waxed
bungs.
Medicinal uses:
• Counter irritant
• Disinfectant
• Proper thyroid functioning
Monograph of
Chlorinated Lime
Name: Chlorinated
lime
Chemical formula:
Ca(OCl) Cl
Molecular weight:
142.98
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
Ca(OH)2 + Cl2 à Ca(OCl2)
Assay: Redox
titration, Iodometric
Ca(OCl)2 + CH3CHOOH à (CH3CHOO)2Ca + Cl2 + H2O
2KI + Cl2 à 2KCl + I2
I2 + 2Na2S2O3 à 2NaI + Na2S4O6
Indicator: Starch
Colour change:
blue -colourless
Storage: Store in
well closed container in a cool place
Medicinal uses:
• Disinfectant
• Bleaching agent
Summary
• Antimicrobial
agents: Kills the microbes
• Antiseptics:
Kill or prevent the growth of microbes
• Disinfectants:
Applied on inanimate objects
• Mechanism of
action: Oxidative, halogenation and protein precipitation
• Monograph analysis
of Potassium permanganate: prepared by, using potassium hydroxide and
manganese di oxide, assayed by iodometric titration in acidic media, medicinally
used as antidote, antiseptic, antimicrobial agent and as strong oxidizing agent
• Monograph analysis
of Boric acid: In lab it is prepared by adding sulphuric acid water mixture
to a solution of borax, assayed by neutralization indirect titration, glycerine
is used in the assay to increase the acidity of boric acid. Medicinally it is
used as germicide and anti-infective agent
• Monograph analysis
of hydrogen per oxide: prepared by electrolysis process of sulphuric acid,
assayed by permangnometric titration in acidic media, medicinally used as
antidote and as strong oxidizing agent
• Monograph analysis
of Iodine: Prepared by sea weed, assayed by redox titration using sodium
thio sulphate as titrant
• Povidone iodine is widely used as anti-bacterial agent