Organophosphorous compounds

It is the commonest poisoning in India
They are used as pesticides in agriculture

The examples are:
•Alkyl phosphates: HETP{Hexa ethyl tetra phosphate}, TEPP{Tetraethyl pyrophosphate}, OMPA{Octa methyl pyrophospharamide}, Malathion
•Aryl phosphates: Paraxon, Parathion, Diazinon{tik-20}, Chlorthion, Methyl parathion

Route :
Ingestion, inhalation or absorption through skin
Fatal Dose :
Varies between 25mg to 1gm for different compounds
Fatal Period :
1/2 to 3 hours
Mechanism of action :
They are irreversible competitive inhibitors of enzyme Acetyl Cholinesterase. Site of action is myo-neural junction snd synapses of ganglion, where normally acetyl choline is liberated from nerve stimulation due to which the impulse is transmitted from motoer nerves to the voluntary muscles and from the sympathetic nerves to the involuntary muscles
This results in accumulation of acetylcholine leading to hyperexcitaion of the muscles.

Clinical Picture :
•Muscarinic like effects:
1.Bronchial effects: bronchospasm, increased secretions, causing dyspnoea, chest pain, cough, cyanosis and pulmonary edema
2.G.I.T: anorexia, nausea, vomiting, abdominal cramps or pain, diarrhea and involuntary defecation
3.Increased sweating
4.Increased salivation
5.Lacrimal glands- increased tears, may be red
6.Bradycardia
7.Meosis of pupils and blurring of vision
8.Frequency of micturition, involuntary micturition

•Nicotine like effects: Fatigue, weakness, cramps, muscular twichings, dyspnoea, cyanosis, pallor, hypertension, arrythmias, paralysis of sphincters

•Actions on CNS: Irritability, restlessness, apprehension, fine tremors of hands, face, lids and tongue, mental cconfusion, stupor convulsions, areflexia, coma and depression of respiratory and cardiac centres

Treatment :
•Decontamination:
1.Patient removed from source
2.remove clothes
3.wash skin and mucous membrane with soap and water
4.gastric lavage
5.emetics

•Care of airway and artificial respiration

•Antidote: Atropine blocks the muscarinic effects. Atropine given initially 2-4mg in moderate poisoning ii.v. or i.m. at 3-10 minutes interval till signs of atropinisation in the form of dry skin, dry mouth, dilated pupils, tachycardia and warmth reappear.

•Cholinesterase reactivators: oxime compounds are used, eg. Diacetyl monoxime, pralidoxime chloride, pralidoxime iodide, pyridine aldoxime methane sulphonate and pyridine aldoxy methiodate given 1-2gmi.v.as 5 percentsolution in isotonic saline. May be repeated 12-24 howebsitey. The therapy should be started early since otherwise there is maturation of the phosphorlyated enzyme. After 24hrs efficacy is less.

•Symptomatic

Organophosphorous compounds

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