ANTI MICROBIAL AGENTS

ANTIMICROBIAL AGENTS

v   These are the substance which help in reducing and preventing infection due to microbes.

v   It can be classified in Specific terminology describes exact mode or mechanism of action

v   Antiseptic

These are substances that are able to kill or prevent the growth of microorganisms. These preparations which are to be applied to living tissues.

v  Disinfectants

These are substances that prevent infection by the destruction of pathogenic micro organisms. These are widely used for non living things (home and hospital etc).

v  Germicides

These are substances which kill microorganisms. More specific terminology like bactericide, fungicide, virucide etc.

v  Bacteriostatic

These are substances which primary function by inhibiting the growth of bacteria. Thus bacteriostatic drugs or agents do not kill but arrest the growth of bacteria.

v  Sanitizers

Disinfectants that are used to maintain general public health standards are termed as sanitizers. Sanitation is mainly concerned with cleaning or washing away the organic matter (saliva, mucous etc )

v  Sterilization

It is the chemical or mechanical process by which an object is completely free from living microbes

v  Astringents

These are drugs which precipitates proteins and form a protective coating when applied to a damaged skin of mucous membrane.

MECHANISM OF ANTIBACTERIAL ACTIVITY

The mechanism of action of inorganic antimicrobials can be divided into three types

v  Oxidation

v  Halogenations

v  Protein precipitation

Oxidation

v  Certain anions and non metals eg. Peroxides, permanganates, halo oxygens and halogens (chlorine and iodine) oxidize the reducing groups present in the microbial protein.

v  The protein after oxidation is not fit for routine metabolic activity and thus the microbe is killed.

v  At higher concentration the drug will also affect the host protein (protein from human body).

Halogenations

v  The hypochlorite anion (OCl^-) present in the antiseptic drug halogenates peptide linkage of the protein molecule.

v  The halogenation changes the shape and specific function of the protein.

R-CONH-    + OCl-  --------à R-CO-N-Cl

Protein precipitation

v  Certain metallic ions having strong electrostatic fields precipitate protein by forming metal protein complex.

v  At sufficient concentration, the metal ion will also react with host as well as microbial protein.

Classification antimicrobial agents

v  The inorganic antimicrobials are classified as

v  Oxidative antimicrobial

v  Hydrogen peroxide, Potassium permanganate, Bleaching powder

v  Iodine and its compounds

v  Iodine solution, Iodine tincture, Povidone iodine

v  Protein precipitants

v  Boric acid, Borax etc

Potassium permanganate KMnO₄

Preparation

1. From Manganese dioxide

v  MnO₂ is fused with excess of KOH in the presence of a free supply of air or in the presence of an oxidising agent such as potassium chlorate.

6KOH  + 3MnO₂  + KClO₃  -à 3K₂MnO₄  +  KCl  +  3H₂O

v  The green residue consisting of potassium manganate is extracted with water. From this KMnO₄ is made by any one of the following 3 methods

1.      By passing carbon dioxide

v  Manganate are converted into KMnO₄ while one of the third is precipitated as manganese dioxide.

3K₂MnO₄  + 2CO₂  -à 2KMnO₄  +  MnO₂  +  2K₂CO₃

2. By passing chlorine gas

v  All the manganate may be converted into KMnO₄ by passing chlorine gas.

2K₂MnO₄  + 2Cl₂  -à 2KMnO₄  +   2KCl

3. By electrolyzing  a warm solution of manganate

v  The solution obtained by any one of the above methods is filtered and concentrated until KMnO₄ separates as crystals.

2K₂MnO₄  + 2H₂O  -à KMnO₄  +  2KOH  + H₂

Properties – It acts as a powerful oxidizing agent

                                    2KMnO₄ à K₂MnO₄  + MnO₂  + O₂

It reacts with HCl, it produce Chlorine

                                    2KMnO₄ + 16HClà 2KCl + MnCl₂ +H₂O  + 5Cl₂

Storage -Stored in a well closed container

Uses

v  Anti infective  ie) disinfectant

v  1 in 4000 solution can be used to mouth wash and gargle

v  Urethritis

v  Antidote in case of poisoning

v  Vertinary antiseptic

v  Crystals are used as first aid treatment for snake bite

v  0.02% stomach wash in the treatment of morphine, opium poisoning

Assay- It is assayed by Redox titration method.

Caution

v   It is a powerful oxidizing agent great care should be observed in handling the substance it produces explosions when it contact with readily oxidising substance  like glycerin.

Boric acid H₃BO₃

Syn: Ortho boric acid

Preparation

1. Laboratory method

                        Borax is mixed with con. H₂SO₄ and allowed to cool. The crystals of boric acid formed is washed with water until free from sulphate and dried

Na₂B₄O₇  + H₂SO₄  + 5H₂O     -à 4H₃BO₄  +    2Na₂SO₄

2. Industrial method

v   Colemanite (Ca₂B₆O₁₁ 5H₂O) is dissolved in boiling water and SO₂ is passed through the solution.

Ca₂B₆O₁₁  + 4SO₂  + 11H₂O     -à  2Ca(HSO₃ )+    6H₃BO₃

v  Among the products calcium bisulphite goes into solution and the less soluble boric acid crystallize on cooling.

Storage- Stored in a well closed container

Uses

v  Germicide. Local anti-infective, Eye and mouth wash

v  Dusting powder, Mild antiseptic

v  Preparation of bioglycerin-used as a suppository base

Hydrogen peroxide (H₂O₂)

Syn: Oxygenated water

Preparation

1. From Barium peroxide

            It is obtained by adding barium peroxide in ice cold water to a calculated quantity of ice cold dil H₂SO₄. The insoluble BaSO₄ is filtered off.

BaO₂  + H₂SO₄     -à BaSO₄  +    H₂O₂

2. Electrolytic method

            It is obtained by electrolysis of ice cold 50% H₂SO_4.   Persulpuric acid is formed which on distillation under reduced pressure gives H₂O_2.

H₂SO₄     -à H₂S₂O₈  +    H₂

H₂S₂O₈   +  2H₂O           -à            2H₂S₂O₄  +    H₂ O₂

3. Sodium peroxide/Barium peroxide

             It is obtained by adding sodium peroxide in ice cold water to a calculated quantity of ice cold dil H₂SO₄ or decomposing barium peroxide with phosphoric acid.

3BaO₂ + 2H₃PO₄     -à Ba(PO₄)₂  +    H₂ O₂

Na₂O₂   +  H₂SO₄           -à     Na₂SO₄  +    H₂ O₂

Storage

Ø  Stored or preserved in a light resistant container with stopper made of glass or plastic resistant to H₂O₂

Ø  It is kept in a dark and cool place

Properties

v  It is a colourless, odourless liquid with acidic taste.

v  The solution decomposes with oxidation or alkali.

                        H₂O₂ à 2H₂O  +  O₂

Uses

v  Strong oxidizing agent

v  Used for bleaching the hair

v  Cleaning cuts and wounds

v  Effective antidote for phosphorous and cyanide poisoning

v   Antiseptic, germicide and deodorant

v  Cleaning ears and removing the surgical dressing

v  1-5% uses as mouth wash to clean root canals and septic sockets

Assay

PRINCIPLE:

v  It is assayed by Redox titration method.

v   It act as an oxidising agent it liberates nascent oxygen readily.

v  Titrated in an acidic medium against potassium   permanganate.

v  KMnO₄ act as a self indicator

v  End point is appearance of pale pink colour.

2KMnO₄ + 3H₂SO₄    à   2MnSO₄ + K₂SO₄ + 3H₂O  + 5[O]

H₂O₂ + [O]  à  H₂O  +  O₂

2KMnO₄ + 3H₂SO₄   + H₂O₂ à   2MnSO₄ + K₂SO₄ + 8H₂O  + 5O₂

ASSAY OF HYDROGEN PEROXIDE:

Procedure

v  Pipette out 1ml of hydrogen peroxide and dilute to 100ml with water.

v  To 10ml of above solution transfer into a conical flask and add 40ml of dilute sulphuric acid and

v  Titrate with 0.1N KMnO₄ and continuing the titration until a pale pink colour appears.

v  Each ml of 0.1N KMnO₄ is equivalent to 0.001701g of hydrogen peroxide.

Chlorinated lime Ca (OCl)Cl

Syn : Bleaching Powder

Preparation

v   Slaked lime is spread in a box-like container and subjected to the action of chlorine gas which is introduced at the top of the chamber and flows through the contents.

v   The temperature maintained below 25°C so that formation of calcium chlorate is brought down.

v  When the absorption of chlorine is complete, which may take about 12 to 24 hours, powdered chlorinated lime is sent into the chamber so that any excess chlorine may be absorbed.

            Ca(OH)₂  +  Cl₂  à  Ca (OCl)Cl  + H₂O

Assay

v   It is assayed by iodometric method. An aqueous suspension of the substance is first treated with excess of potassium iodide and acetic acid. Acetic acid, like other acids, liberates chlorine from chlorinated lime as below.

Ca(OCl)Cl + 2CH₃COOH  à (CH₃COO)₂Ca +  HOCl +HCl

                        HOCl + HCl àCl₂ + H₂O

v  The liberated chlorine displaces an equivalent amount of iodine from potassium iodide

            2KI + Cl₂à KCl  +I₂

v   This iodine is titrated against 0.1N sodium thiosulphate using starch mucilage as indicator.

            2 Na₂ S₂ O₃ + I₂à Na₂ S₄ O₆ + 2NaI

Properties

v  It is a white or granular powder having a odour of chlorine consisting of "calcium chlorohypochlorite", which is intermediate between calcium chloride and calcium hypochlorite, Ca(OCl)₂.

v  When exposed to air, it absorb moisture and decomposed.

v  With water, it shows bleaching and oxidizing properties

Ca(OCl)Cl + CO₂ + H₂O à CaCO₃ +  HOCl +HCl

HOCl + HCl àCl₂ + H₂O

Uses

v  It is used in latrines and other places because chlorine is produced as given above and sterilizes the places.

v  It is used mainly for its disinfecting properties and as a bleaching agent.

Storage

v   It has varying amounts of calcium hydroxide and moisture. Although it becomes moist on exposure to air, it is not deliquescent.

v  When It is exposed to the air, it slowly decomposes. And for this reason chlorinated lime should be stored only in tightly stoppered bottles.

Iodine (I₂)

Preparation

v  Iodine is manufactured by extracting kelp (Seaweed’s ash) with water.

v  The solution is concentrated when the sulphate and chloride of sodium and potassium gets crystallized out and the liquid containing soluble sodium and potassium iodide is added with sulphuric acid, the sulphur is liberated and settle down.

v  The mother liquid is decanted and to this add MnO₂ and the iodine distils over.

2NaI+3H₂SO₄+ MnO₂ à MnSO₄ + 2NaHSO₄ + I₂ + 2H₂O

v  Iodine is also found in the brine oil wells

Properties

v  Iodine is heavy, bluish-black, rhombic prism.

v  It has peculiar odour and sublimation property.

v  It is insoluble in water and soluble in alcohol, chloroform and ether.

v  It reacts with some non-metals and many metals.

                        2P  + 3I₂  à 2PI₃

                        Fe  + I₂  à FeI₂

v  Aqueous solution of Iodine oxidizes the reducing agents

                        H₃AsO₃  +I₂  + H₂O  à 2HI  +  H₃AsO₄

                        H2S + I2  à 2HI  + S

                        2Na₂S₂O₃  + I₂  à 2NaI  +  Na₂S₄O₆

v  It reacts with alkali to form an iodide and iodate.

                        3I₂  +  6NaOH  à 5NaI  +  NaIO₃  +  3H₂O

Assay

v  Iodine is assayed by Redox method.

Iodine preparations

1. Aqueous Iodine solution (Lugol’s solution).

v  It is 5% w/v iodine and 10% w/vpotassium iodide in purified water.

v  It is prepared by dissolving iodine and KIin100 ml water with trituration or shaking and made up to 1000ml with purified water.

Uses :

v  It acts as a good source of iodine and is taken internally.

v  It  possess germicide and fungicide action and does not produce irritation on cuts and wounds.

Storage – In well closed glass or plastic containers.

2. Weak Iodine solution (Iodine tincture).

v  It is 2% w/v iodine and 2.5% w/v potassium iodide in 50% alcohol

v  KI and iodine are first dissolved in sufficient alcohol(50%) and made up to 1000ml with alcohol(50%).

Uses :

v  It acts as a good source of iodine and is taken internally.

v  It  possess germicide, fungicide and antiseptic action on cuts and wounds.

Storage – In well closed glass or plastic containers.

3. Strong Iodine solution

v  It is 10% w/v iodine and 6% w/v potassium iodide in  purified water and 90% alcohol

v  KI and iodine are first dissolved in purified water and add sufficient alcohol(90%) to produce1000ml.

Uses :

v  It  possess antiseptic action.

Storage – In well closed glass or plastic containers.

4. Povidone - Iodine solution

v  It is aqueous solution of povidone-iodine.

v  It is a complex produced by interaction between iodine and povidone (polyvinyl pyrrolidine).

v  The complex is having 10% w/v of available iodine.

properties :

v  It is yellowish brown amorphous powder with iodine smell

v  It is soluble in water and alcohol.

v  Its aqueous solution is having acidic pH.

Uses

v  10% povidone-iodine is used as bactericidal

v  It is also used as disinfection of skin, mouth or wounds.

v  It is also effective in the management of burns and cuts.

Storage – In well closed glass or plastic containers.