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
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 –> 2K2MnO4 + 2H2O

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

K2MnO4 + 3Cl2 –> 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 –> 6K2SO4 + MnSO4 + 8H2O +
5I2

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:

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 –> H2O2 + Na2SO4

2. By electrolysis of 50 percent ice cold sulphuric acid

2H2SO4 –> H2S2O8

H2S2O8 + 2H2O –> 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 –> 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 +
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 –> 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

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

Also, Visit:

B. Pharma Notes | B. Pharma Notes | Study material Bachelor of Pharmacy pdf

B. Pharma Handwritten Notes

B. Pharma PDF Books

B. Pharma Lab Manual

D. Pharma Lab Manual

B. Pharma 8th Semester Previous Year Question Paper

D. Pharma Notes

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