Autonomic Nervous Systems
Physostigmine is the antidote for poisoning with antimuscarinic drugs (e.g atropine). Another AChE inhibitor, neostigmine, is not suitable. That is because neostigmine cannot overcome the adverse effects of the antimuscarinic drug in or on which of the following? (AIPG 2011)
|A||Central nervous system|
a. Physostigmine is basically the only clinically useful AChE inhibitor that gets into the brain, a major target of atropine/antimuscarinic poisoning.
b. That is because it lacks the quaternary (charged at virtually all pH values likely to be found in a living person) structure that nearly all the other common alternatives possess, and lacking that structure it can cross the blood-brain barrier.
c. Alternatives such as neostigmine, pyridostigmine, and others, will combat peripheral effects of atropine poisoning, just as physostigmine will.
d. Unfortunately, some of the CNS manifestations (e.g., severe fever, leading to seizures) contribute greatly to the morbidity and mortality associated with high doses of antimuscarinics, and the quaternary agents simply will not combat them in the CNS.