Antimicrobial agents – Pharmaceutical Inorganic Chemistry B. Pharma 1st Semester

Antimicrobial agents

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

• 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 –> 2K2MnO4 + 2H2O

KOH + MnO2 + KCLO3 –> KCl + K2MnO4 + 3H2O

K2MnO4 + 3Cl2 –> KMnO4 + KCl

Properties of potassium permanagante:


• 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



Iodometric titration, Direct titration 

2KMnO4 + 10KI + 8H2SO4 –> 6K2SO4 + MnSO4 + 8H2O +

I2 + 2Na2S2O3 –> 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 –> 4H3BO3 + Na2SO4

Properties of boric acid:


• 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 –> H2O2 + Na2SO4

2. By electrolysis of 50 percent ice cold sulphuric acid

2H2SO4 –> H2S2O8

H2S2O8 + 2H2O –> 2H2SO4 + H2O2

Properties of hydrogen peroxide:


• 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 –> 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 –> MnSO4 + 2NaHSO4 + I2 +

Properties of Iodine:


• 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 –> 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 –> Ca(OCl2)

Assay: Redox titration, Iodometric

Ca(OCl)2 + CH3CHOOH –> (CH3CHOO)2Ca + Cl2 + H2O

2KI + Cl2 –> 2KCl + I2

I2 + 2Na2S2O3 –> 2NaI + Na2S4O6

Indicator: Starch

Colour change: blue -colourless

Storage: Store in well closed container in a cool place

Medicinal uses:

• Disinfectant

• Bleaching agent


• 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

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