Classification of Poisons

 CLASSIFICATION OF POISON

Human poisoning can be classified two into broad divisions - 

Acute poisoning : It may be self or accidental poisoning in which symptoms appear suddenly soon after the consumption of poison. These symptoms increase in severity and may cause death if not attended. 

Chronic poisoning : It slowly develops from a drug built up over absorption than has left it through metabolism and excretion. There is disappearance of symptoms on removal of patient from further exposure. 

image : poison

Classification for Poisons :

Corrosives - 

Mineral acids - HCl, H2SO4, HNO3

Organic acids - Acetic, Carbolic

Strong alkalis - NaOH, KOH

Irritants - 

Inorganic :

Non- metallic - Phosphorus, chlorine, bromine

Metallic - Arsenic, mercury, lead

Organic :

Vegetable - Castor oil seed, aloes

Animal - Snakes, insect bites, cantharides

Mechanical - Diamond dust, powdered glass 

Neurotics :

Cerebral - Opium, alcohols, datura, cannabis

Spinal - Strychnine 

Cardiac - Aconite, digitalis, tobacco

Asphyxiants - CO2, CO, coal gas

Acting on peripheral nerves - Tubocurarine

General treatment of poisoning :

• Removal of unabsorbed/ absorbed poison 

• Antidote treatment 

• Symptomatic treatment directed towards :-

1. Drawing out the poison : Vomit, purge, diuresis 

2. Neutralization : Physical, chemical, physiological, pharmacological and clinical antidote

3. Protection of various organs from toxic effects of poison 

4. Symptomatic relief 

5. Viatalising the vital centres : Cardiac, vasomotor and respiratory centres

1. Removal of Unabsorbed Poisons : Following methods can be used for removal of unabsorbed - 

Emetics : If the patient is not vomiting, give 15g of sodium chloride dissolved in one glass of water. Repeat till vomit is clear. If unsuccessful, then 2 teaspoonful of powder mustard in glass of water will arouse a vomit. It not, then ipecacuanha powder 1 - 2g, finally apomorphine hydrochloride injection can be used to induce vomiting. This injection is contraindicated in morphine poisoning. Mechanical irritation of the throat by finger, tongue depressor or spoon evokes instaneous vomiting. 

Gastric Lavage : This is an established method for the removal of any unabsorbed poison from the stomach. Since the stomach contents pass out in 3 - 4 hours, a stomach wash proves useless after this time interval. However, in opium poisoning this is not the case. By whatever channel, it may have been administered, it is finally excreted through the stomach. Hence, gastric lavage should be carried out in all cases of opium poisoning. 

Solution and substances used for gastric lavage include - 

• Saline solution - 1 teaspoonful of sodium chloride in a tumblerful of warm water 

• Warm water 

• KMnO4 Solution

• For alkaline wash - 5% w/v sodium bicarbonate solution 

• Sodium thiosulphate and dimercaprol solutions are also used for the treatment in toxic metallic poisoning 

Miscellaneous :

• Contact poison (if sprayed on skin, eye or wound) can be removed by washing with plain water 

• If a poison can be removed by means of incision and suction 

• Inhaled poison like carbon monoxide or other poisoning can be removed by putting the patient in fresh air or by giving artificial respiration 

Removal of absorbed poison : Elimination of absorbed poison can be enhanced by increasing the urine output by means of diuretic like mannitol, fursemide or by adjusting pH of urine, e.g - acidic drugs are excreted faster in alkaline urine and alkaline drugs in acidic urine. Peripheral dialysis can be done to remove absorbed poison. 

2. Antidote Treatment 

 It is an agent that counteracts a poison. They can be classified on the basis of mechanism of antidote action :

• Physiological : It counteracts the effects of a poison by producing other effects. Bemegride is used in barbiturate poisoning (opposite action). Caffeine is used in morphine poisoning. 

• Chemical : It changes the chemical nature of a poison. For example, sodium thiosulphate used in cyanide poisoning, converts the toxic cyanide into non- toxic thiocyanate which is excreted easily. 

• Mechanical : It prevents the absorption of the poison into the body. Kaolin and charcoal absorb the poison prior to absorption across the intestinal wall. Fats, oils and egg albumin also hinder the absorption of poison. 

 Absorption can also be prevented by using general antidote (combination of MgO, Tannic acid and activated Charcoal in ratio of 1:2:2.

 All these substances are suspended in glassful of warm water and given orally. This is universally useful and harmless. 

 In addition to above antidotes, there are some specific antidotes. These includes - 

• Nalorphine used in morphine poisoning 

• Dimercaprol (BAL) used in arsenic and mercury poisoning. Heavy metals like arsenic and mercury have great affinity for - SH (Sulfahydryl group) and so they combine with enzymes containing this group and inactivate them. BAL has many - SH group, therefore, combines with arsenic and mercury and protects the - SH group present in enzymes. The complex formed from dimercaprol and heavy metal is stable and excreted easily. 

• Ethylene diamine tetraacetic acid (EDTA) : It is given in lead poisoning. It forms stable lead - EDTA complex which is non- toxic, soluble and rapidly excreted. 

• Penicilliamine (cuprimine) : It is used in copper, lead an mercury is attributed to presence of - SH group in it. The chelating effect of penicilliamine. 

• Desferrioxamine : It is used for treatment of iron poisoning. It accelerates the removal of iron from the body. 

• Atropine is used in the poisoning of physostigmine 

3. Symptomatic Treatment

 It involves assisted mechanical ventilation, maintenance of blood pressure by vasopressor agent, nutrition by intravenous glucose saline and prevention of secondary infection.