Antidotes | Pharmaceutical Chemistry

Antidotes are drugs designed to counteract toxins/poison/xenobiotics.

An antidote can act in a number of ways like

  • Limiting absorption
  • Sequestering the poison
  • Inhibiting metabolism to a toxic metabolite
  • Promoting distribution from tissues
  • Displacing the poison from a receptor or competing for the receptor
  • Counteracting the toxic effect
  • Enhancing detoxification

Classification of Antidote

Pharmapedia, Classification, Antidote, Mechanical antidotes, Chemical Antidotes, Physiological antidote,
Classification of Antidotes

According to mechanism of action antidote are classified below

Physiological antidotes

Physiological antidote also called antagonist. The produce the effect opposite to that of the poison. They are used after some of poison is observed in the circulation.
Sodium nitrite (used in cyanide poisoning), atropine and Physiostigmine are two antidotes for each other.

Chemical antidotes

These antidotes react by combining with the poison and change its chemical nature by converting the poison into inactive or harmless compounds.
Sodium thiosulfate (it convert the systemic toxic cyanide into non toxic thiocyanate), EDTA (chemical agent for heavy metal poisoning).

Mechanical antidotes

They act by preventing the absorption of poison into the body or expel out the poisoning by emesis or eliminate through urine.
Activated charcoal absorb the poison prior to absorption into the systemic circulation form intestinal wall.
Copper sulphate, magnesium sulphate and sodium monohydrogen phosphate in activate the poison prior to absorption and precipitate the toxic material as in insoluble salt

Antidote for selected inorganic poison and drug overdose

Poison/Drug OverdoseAntidoteMechanism
Acid (Corrosive)Antacid or Weak Alkali (Milk of magnesia), Avoid Induce vomitingChemical Antagonism, Acid base neutralization
Alkali (Caustics)Weak Acid (Lemon juice/diluted vinegar) Chemical Antagonism, Acid base neutralization
Iron SaltsDesferroxamineChelation
Copper & LeadsPenicillamine Chelation
Mercury SaltDimercaprol (BAL) Chelation
Antidote for selected inorganic poison and drug overdose

Sodium Nitrite

M.F. : NaNO2; Mw; 69


Most common suitable method
Absorbing of nitrogen oxide gas (NO) by sodium carbonate solution. The solution is concentrated to crystallize out the product.
2Na2CO3 + 4NO + O2 → 4NaNO2 + 2CO2


  1. Colourless to slightly yellow crystals, odourless, saline taste.
  2. It is deliquescent. Absorb moisture and slowly gets oxidized to sodium nitrate.
  3. Soluble in water.
  4. It is a reducing agent.


  • As reducing agent when combine with Sodium carbonate to form anti-Rust tablets. Anti-Rust tablets are used to prevent rusting of surgical instruments.
  • As antidote in the treatment of cyanide poisonings

Cyanide poisoning & its treatments

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