Poison And Antidotes

Introduction

Poisons are substances that, when ingested, inhaled, or absorbed, can cause harm to the body. They may be accidental, occupational, suicidal, or criminal in nature. Common causes of poisoning include heavy metals, drug overdose, and exposure to toxic chemicals. Notable types include heavy metal poisoning, cyanide poisoning, and snake venom. Antidotes are substances that specifically react with ingested poisons or toxic substances, neutralizing their effects. Examples include sodium thiosulphate for cyanide poisoning and EDTA as a chelating agent for heavy metal poisoning. Prompt identification of the ingested poison is crucial for selecting the appropriate antidote.

Table of Contents

Types of antidotes

Antidotes can be classified based on their mechanism of action as follows.

Physiological antidote: It acts by producing the effect opposite to that of poison, or counteracts the effect of poison physiologically.

Chemical antidote: It acts by combining with the poison and changing its chemical nature so the poison cannot act any more.

Mechanical antidote: It acts by preventing the absorption of poison in the body or expelling out the poison by emesis or elimination through urine.

Heavy metal poisoning

Heavy metal poisoning occurs due to intake of over dose or due to their incomplete metabolism in the body. Common heavy metals which cause poisoning are salts of arsenic, lead, mercury, iron and cadmium. The most widely used method to antagonize heavy metal poisoning, is to form specific chelate or complex form with it.

In heavy metal poisoning, activated charcoal is administered to absorb the poison. After this, emetics are administered. This eliminates the possibility of any poison remaining in the stomach, being absorbed in the circulation. If poison is being absorbed in the circulation, some effective antidotes are used in heavy metal poisoning. Some inorganic compounds like activated charcoal, kaolin, copper sulphate and magnesium sulphate are used as antidotes in heavy metal poisoning.

Activated charcoal

Preparation: commercially it is obtained by residue during destructive distillation of various organic matters. It is also obtained from burning organic materials in a special manner. The coarse residue is powdered.

Properties

Fine black powder
Odourless
Tasteless
Smooth in touch
Free from gritty particles
Insoluble in water

Action and uses

It is a general type of adsorbent used in poisoning
It adsorbs heavy metals, hypnotics and sedatives like alkaloids
It also adsorbs gases like carbon monoxide, carbon dioxide, nitrous oxide, etc.
It is used in the ratio of 5:1 or 10:1 (carbon to poison)
It is administered in the form of tablets

Cyanide poisoning

Cyanide poisoning results from exposure to various forms of cyanide. Early symptoms include headache, dizziness, fast heart rate, shortness of breath, and vomiting. This phase may then be followed by seizures, slow heart rate, low blood pressure, loss of consciousness, and cardiac arrest. Cyanide compounds interfere with cellular respiration, preventing the body’s tissues from using oxygen. Poisoning is relatively common following breathing in smoke from a house fire. Other potential routes of exposure include workplaces involved in metal polishing, certain insecticides, the medication sodium nitroprusside, and certain seeds such as those of apples and apricots. Treatment involves supportive care, 100% oxygen, and the use of hydroxocobalamin (vitamin B12a) as an antidote. Historically, cyanide has been used for mass suicide and genocide by the Nazis.

Antidotes used in cyanide poisoning

In case of cyanide poisoning, sodium nitrite and sodium thiosulphate injections are given to counteracts the effects of cyanide poison. Sodium thiosulphate reacts with cyanide ions and converts into sodium thiocyanate which is less toxic than cyanide. While sodium nitrile reacts with ferrous iron of hemoglobin and converts into ferric iron of methemoglobin and thus reduces the concentration of cyanide ions.

Sodium Nitrite

Chemical Formula: NaNO₂
Description: Nitrous acid, sodium salt
Purity: Contains not less than 97.0% and not more than 101.0% of NaNO₂ (calculated on the dried basis).
Packaging and Storage: Preserve in tight containers. Store at 25°C, with excursions permitted between 15°C and 30°C.
Identification: A solution of sodium nitrite responds to tests for sodium and nitrite.
Loss on Drying: Dry it over silica gel for 4 hours; it loses not more than 0.25% of its weight.
Heavy Metals: Dissolve 1 g in 6 mL of 3 N hydrochloric acid, evaporate to dryness, and determine heavy metals (limit: 0.002%).
Residual Solvents: Meets the requirements.
Assay: Each mL of 0.1 N potassium permanganate is equivalent to 3.450 mg of NaNO₂.

Sodium Thiosulfate

Description: Nitrous acid, disodium salt, pentahydrate. Also known as disodium thiosulfate pentahydrate.
Chemical Formula: Na₂S₂O₃·5H₂O
Anhydrous Form: Molecular weight of 158.11 g/mol 1.
Pentahydrate Form: Molecular weight of 248.19 g/mol 1.
Purity: Contains not less than 99.0% and not more than 100.5% of Na₂S₂O₃, calculated on the anhydrous basis.
Packaging and Storage: Preserve in tight containers.
Identification:
- A: A solution (1 in 10) responds to iodine TS by discharging the color.
- B: A solution (1 in 10) passes tests for sodium and thiosulfate.
Water Content: Dry about 1.0 g in a vacuum at 40 to 45°C for 16 hours; it loses between 32.0% and 37.0% of its weight.
Calcium Content: Dissolve 1 g in 20 mL of water, add ammonium oxalate TS: no turbidity should be produced.
Heavy Metals: Dissolve 1 g in 10 mL of water, add 5 mL of 3 N hydrochloric acid, evaporate, and determine heavy metals (limit: 0.002%).
Residual Solvents: Meets the requirements.
Assay: Each mL of 0.1 N iodine is equivalent to 15.81 mg of Na₂S₂O₃.

Summary

Poisons are substances that, when ingested, inhaled, or absorbed, can cause harm or be fatal. They can come from various sources, including chemicals, toxins, plants, or certain foods. Antidotes, on the other hand, are substances that specifically react with ingested poisons or toxic substances, neutralizing their effects. They either convert the poison to non-toxic forms or counteract its impact. Antidotes can act through various mechanisms, such as complex formation, metabolic conversion, and physiological reversal. They play a crucial role in treating poisoning cases. Common types of poisoning include heavy metal poisoning, cyanide poisoning, and insecticide poisoning. Sodium thiosulfate and activated charcoal are examples of antidotes. Remember that prompt identification of the ingested poison is crucial for selecting the appropriate antidote.