Poison and Antidote - Pharmaceutical Inorganic Chemistry B. Pharma 1st Semester

Poison and Antidote


• Antidote

• Cyanide poisoning

• The monograph analysis of: Sodium nitrite, Sodium thio sulphate, Activated charcoal

Learning Objectives

At the end of this lecture, the student will be able to:

• Describe antidote

• Cyanide poisoning

• Explain the monograph analysis of: Sodium nitrite, Sodium thio sulphate, Activated charcoal


It may be defined as those substances, which react specifically with an ingested poison or toxic substance or an over dosage of a potent drug. They act either by neutralizing the poison or its toxic effect or pharmacologically or chemically by converting them to non-toxic or less toxic forms.

An antidote is an agent which counteracts:

• A poison

• Over dosage of a potent drug

• Toxic substance

Mechanism of Action of Antidotes

Antidotes act by different mechanism. The mechanisms of action of antidotes are given below:

1) Complex formation

2) Metabolic conversion

3) Prevention of toxic metabolite formation

4) By changing the physio-chemical nature of toxicant

5) Promotes return to normal function by repairing a defect or enhancing a function that corrects the effects of poison

Classification of Antidotes

Depending on their action, antidotes are classified as:

1) Chemical Antidotes: They act by usually by combining with the poison and thus changing the chemical nature of the poison so that it becomes inactive.

Eg: Sodium thio sulphate converts systemically toxic cyanide to nontoxic thio cyanate.

2) Physiological Antidotes: They act by producing the effect opposite to that of poison, or counter act the effect of poison physiologically.

Eg: Sodium nitrite converts hemoglobin to meth hemoglobin and prevents binding of cyanide ion.

3) Mechanical Antidotes: They act by usually preventing the absorption of poison in the body or expel out the poison by emesis or elimination through urine.

Eg: activated charcoal absorbs the toxic or poisons before it gets absorb across the intestinal wall.

Cause of Poisoning

Poisoning of the body can be ascertained due to various reasons:

 The most common poisoning occurs due to environment contamination with heavy metals. This has lead to food and water contamination.

 The poisoning also occurs because of insecticides or pesticides.

 The poisoning can also occur due to excess use of drugs.

 The poisoning can also due to intentionally also to commit suicide.

Antidote is here generally discussed on heavy metals and cyanide poisoning.

Different types of poisoning

• Cyanide poisoning

• Heavy metal poisoning

• Food poisoning

• Water poisoning

Cyanide poisoning

Mechanism of action of Cyanide

• Inhibits cellular respiration – Cytochrome oxidase

• Tissues cannot utilize oxygen

• Tissues die

• Finally the person dies

Mechanism of action of drugs used for cyanide poisoning

Clinical Effects of Cyanide posioning


– Headache

– Dizziness

– Seizures

– Coma

• Cardiovascular

– Hypertension, bradycardia

– Hypotension, later in course

– Cardiovascular collapse

Treatment for cyanide poisoning

The inorganic compound used are Sodium nitrite followed by Sodium thio sulphate

For cyanide poisoning two inorganic compounds, sodium nitrite and sodium thio sulphate is administered intravenously. The action of these two compound as follows:

Sodium nitrite is able to convert haemoglobin to meth haemoglobin, thus cyanide poisoning of Cytochrome enzyme is prevented. This process is reversible. So immediately after the injection of sodium nitrite a slow intravenous infusion of sodium nitrite is given. The nitrite ion reacts with the cyanide ion and converts to nontoxic thiocyanate, which is eliminated out through urine.

Monograph of Sodium nitrite

Name: Sodium nitrite

Chemical formula: NaNO2

Molecular weight: 68.09

Standards: Sodium nitrite contains not less than 97 per cent and not more than 101.0 per cent of NaNO2

Method of Preparation:

2Na2CO3 + 4NO + O2 à 4NaNO2 + 2CO2

Medical uses:

• Antidote for cyanide poisoning

• Vasodilator

Monograph of Sodium thiosulphate

Name: Sodium thiosulphate

Chemical formula: Na2S2O3,5H2O

Molecular weight: 248.2

Standards: Sodium Thiosulphate contains not less than 99.0 percent and not more than 101.0 per cent of Na2S2O3,5H2O

Synonym: sodium hyposulphate or “hypo” or antichlor

Method of preparation:

2Na2CO3 + H2O + 2SO2 à NaHSO3 + CO2

NaHSO3+ Na2CO3 à 2Na2SO3 + H2O + CO2

Na2SO3 + S à Na2S2O3

6 NaOH + 4S à 2Na2S + Na2S2O3 + 3H2O

Properties of sodium thiosulphate:


• Colourless large crystals or a coarse, crystalline powder

• Odourless

• Deliquescent in moist air and effloresces in dry air at temperature above 33º C

• It dissolves in its water of crystallisation at about 49º C

Test for purity:

Appearance of solution



Heavy metals



Sulphates and sulphites

Monograph of Sodium thiosulphate cont…

Assay: principle

Iodimetric titration

2Na2S2O3 + I2 à 2NaI + Na2S4O6

Indicator: starch

Colour change:  colourless to pale blue

Storage: store protected from moisture

Medicinal uses:

• Anti-dote for cyanide poisoning

• Parasitic skin diseases

Monograph of Activated charcoal

Name: Activated charcoal

Activated Charcoal is obtained from vegetable matter by suitable carbonisation processes intended to confer a high adsorbing power

Synonyms: Universal antidote, Decolorising Charcoal

Method of Preparation:

It is prepared from natural vegetable

It involves the following steps:

Step 1. Wood, coconut shell heated at 6000C in absence of air à Vegetable Charcoal

Step 2. Vegetable Charcoal heated at 5000C to9000C in Exposed to air/ steam/ carbon di oxide/sulphuric acid/Phosphoric acid/ zinc chloride à Activated charcoal

• Storing in suitable container

Test for purity

• Copper

• Chlorides

• Zinc

• Acid-soluble substances

• Acidity or alkalinity

• Lead

• Loss on drying

• Ethanol-soluble substances

• Absorbing power

• Uncarbonised constituents

• Sulphated ash

• Sulphide

• Alkali-soluble coloured matter

• Sulphates

Storage: Store protected from moisture

Medicinal uses:

• Adsorbent in food and alkaloidal poisoning

• Absorbs various gases and toxins

• Dyes and decolourising agent

Antidote is here generally discussed on heavy metals and cyanide poisoning.

Heavy metals poisoning

The common heavy metals responsible for poisoning are the salts of arsenic, lead, mercury, iron and cadmium. Heavy metals poisoning occur because of over dose intake or because of their incomplete metabolism on the body. The mechanism involved in treating the heavy metal poisoning is by administering the drugs, which form a chelate with poison, and converting them into the non-toxic substance and eliminating out from the body through oral or through urine.

The initial treatment for heavy metal poisoning is administration of activated charcoal for absorbing the heavy metal or poison and followed by drugs, which causes emesis so that the poison is removed from circulation.

Some of the inorganic compounds used as antidotes for heavy metal poisoning are copper sulphate, magnesium sulphate, sodium phosphate, etc.

Besides these there are organic compounds which are widely used. They are:

1. D-Pencillamine: Used for copper, magnesium, and lead poisoning.

2. Deferoxamine: Against iron.

3. Dimercarpol: Arsenic, gold, mercury poisoning.

4. Succimer: Arsenic, lead, mercury poisoning.

5. Calcium disodium EDTA: Universal antidote as it forms complex with most of the heavy metals. It is not much used because of its side effect. The universal antidote is activated charcoal.


•Antidote: used against toxic substances, poisoning and overdose of potent drug

• Cyanide poisoning treatment: Sodium nitrite and sodium thio sulphate

• Activated Charcoal: Universal antidote, as it has good absorbing property


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