Treatment of Anticholinesterase Poisoning

The first step in treatment of anticholinesterase poisoning should be injection of increasing doses of atropine sulfate to block all adverse effects resulting from stimulation of muscarinic receptors. Since atropine will not alleviate skeletal and respiratory muscle paralysis, mechanical respiratory support may be required.

If the poisoning is due to an organophosphate, prompt administration of pralidoxime chloride will result in dephosphorylation of cholinesterases in the periphery and a decrease in the degree of the blockade at the skeletal neuromuscular junction. Since pralidoxime is a quaternary amine, it will not enter the CNS and therefore cannot reactivate central cholinesterases. In addition, pralidoxime is effective only if there has been no aging of the phosphorylated enzyme. Pralidoxime has a greater effect at the skeletal neuromuscular junction than at autonomic effector sites.

^ Study Questions

1. A young patient is being treated for myasthenia gravis, which requires frequent adjustment of the optimal dose of neostigmine. The patient is challenged with edrophonium to evaluate the effectiveness of the cholinesterase inhibition. Optimal dosing will be indicated by

(A) An increase in muscle strength

(B) A decrease in muscle strength

(C) No change in muscle strength

2. A young man broke his leg in a skiing accident, causing severe muscular spasm that necessitated relaxation of the muscle with a competitive nicotinic receptor antagonist before the fracture could be set. At the end of the orthopaedic procedure, the doctor restored neuromuscular transmission by administering:

(A) Succinylcholine (b) Carbachol

(C) Physostigmine

(D) Neostigmine

3. A patient has developed glaucoma that is refractory to noncholinergic therapies. You decide to prescribe eyedrops containing pilocarpine, but you are concerned about the patient's ability to self-administer the drops. The most sensitive indicator of excessive administration of pilocarpine is

(A) An increased heart rate

(B) A decreased heart rate

(C) Mental confusion

(D) Constriction of the pupil

4. An 80-year-old man is increasingly forgetful, and his wife is afraid he is developing Alzheimer's disease. You are considering prescribing an anti-AChE drug to see if this will decrease his forgetfulness. Before making this prescription, you want to be sure that these drugs are suitable given the patient's medical history. Of the possible preexisting conditions listed below, you should be least concerned about

(A) Asthma

(B) Weak atrioventricular conduction

(C) Glaucoma

(d) Obstruction of the GI tract

5. The choice of route of administration plays an important role in the actions of directly acting choli-nomimetics. An adverse effect of choline esters that may be avoided by selection of an appropriate route of administration is:

(A) Bradycardia

(B) Hypotension (c) Delirium

(D) Sweating

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