DEFINITIVE TREATMENTOF

ORGANOPHOSPHORUS POISONING

Atropine

Cholinesterase reactivators (Oximes)

Drugs used in definitive treatment:

(a)ATROPINE

Anti cholinergic drug.

Objective : To block the muscarinic receptors until the organophosphate is metabolised away from the body.

Atropine : Adult dose : 2-5mg i.v. repeated every 5 min doubling the initial dose.

Children : 0.05-0.1mg/kg

Given till signs of atropinization appear.

Continued treatment: maintenance dose (30% of atropinization dose) for 1-2 weeks.

(b)CHOLINESTERASE REACTIVATORS

Oximes are used to restore neuromuscular transmission.

If more reactive OH groups in the form of oximes (Generic formula R-CH=N-OH) are provided reactivation occurs more faster.

Eg: Pralidoxime ( 2-PAM)

Action of Pralidoxime (2-PAM)Attaches to the anionic site of the enzyme.Oxime end reacts with the phosphorus atom

attached to the esteratic site.Oxime-phosphonate form and diffuse away.Reactivated ChE remain. Treatment should be started within 24 hours

before the phosphorylated enzyme undergoes ‘Aging’ and become resistant to hydrolysis.

It is ineffective to carbamate poisoning as in that case the anionic site of the enzyme is not free.

It is rather contraindicated because it has weak anti-ChE activity of its own.

Injected i.v. slowly in a dose of 1-2g.

Doses may be repeated according to need.

Use of oximes in OP poisoning is secondary to that of Atropine.

OTHER OXIMES:

Obidoxime: more potent than pralidoxime

Diacetyl-monoxime (DAM): Lipophilic; so if the OP poisoning symptoms are more central DAM is used as it can cross the blood brain barrier.