Drugs affecting the autonomic nervous system ( Physostigmine, Echothiophate and Pralidoxime)
Physostigmine:
Structure:
Physostigmine contains a tertiary amine.
Activity:
Physostigmine has both muscarinic and nicotinic activity.
Can physostigmine penetrate the brain?
Yes, physostigmine can penetrate the central nervous system (CNS) because it is uncharged.
Pharmacological action:
Physostigmine stimulates pupil constriction in a process called miosis and it has a wide range effect.
Uses:
1- systemically: antidote for TCA and atropine.
2- locally: glucoma and high intraocular pressure (miotic agent)
Side effect:
1- Physostigmine can penetrate the central nervous system because it is not charged, so it is likely to cause several problems in the central nervous system, most notably convulsions.
2- skeletal muscle paralysis.
Echothiophate:
Structure:
It is an organophosphate that covalently binds to the serine-OH group at the active site of acetylcholinesterase.
Activity:
Echothiophate has both muscarinic and nicotinic activity.
Can Echothiophate penetrate the brain?
Yes, Echothiophate can penetrate the central nervous system (CNS) because it is uncharged.
Pharmacological action:
The Echothiophate can produce narrowing of the pupil of the eye stronger than the previous medicines (intense miosis).
Uses:
It is used first-line agent in the treatment of glaucoma.
Side effect:
1- Cataract
2- Breathing difficulties ( Because cholinergic agonists narrow the bronchial tubes)
3- Convulsions (Because Echothiophate can penetrate the central nervous system)
Pralidoxime
Structure:
It breaks the bond between the Echothiophate and Acetylcholinestrase. So, it can reactivate inhibited acetylcholinesterase.
Can Pralidoxime penetrate the brain?
No, Pralidoxime can’t penetrate the central nervous system (CNS) because it is charged.
Pharmacological action:
It is a weak acetylcholinesterase inhibitors.
Uses:
Pralidoxime works to reverse the effect of Echothiophate (in other words, it is used as an antidote to Echothiophate).