Parasympathomimetic drug
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Structure activity relationships for parasympathomimetic drugs[7]
For a cholinergic agent, the following criteria describe the structure activity relationship:
- Ing's Rule of 5: there should be no more than five atoms between the nitrogen and the terminal hydrogen for muscarinic (or cholinergic) activity;
- the molecule must possess a nitrogen atom capable of bearing a positive charge, preferably a quaternary ammonium salt;
- for maximum potency, the size of the alkyl groups substituted on the nitrogen should not exceed the size of a methyl group;
- the molecule should have an oxygen atom, preferably an ester-like oxygen capable of participating in a hydrogen bond;
- there should be a two-carbon unit between the oxygen atom and the nitrogen atom.
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Pharmaceuticals/Supplements
Direct-acting
These act by stimulating the nicotinic or muscarinic receptors.
- Choline esters
- Acetylcholine (all acetylcholine receptors)
- Bethanechol (M3 receptors)
- Carbachol (all muscarinic receptors and some nicotinic receptors)
- Methacholine (all muscarinic receptors)
- Plant alkaloids
Indirect-acting
Indirect acting parasympathomimetic substances may be either reversible cholinesterase inhibitors, irreversible cholinesterase inhibitors or substances that promote ACh release or anti-adrenergics. The latter inhibits the antagonistic system, the sympathetic nervous system.
- Reversible cholinesterase inhibitors
- Donepezil
- Edrophonium
- Neostigmine
- Physostigmine
- Pyridostigmine
- Rivastigmine
- Tacrine
- Caffeine (non-competitive)
- Huperzine A
- Irreversible cholinesterase inhibitors
- Echothiophate
- Isoflurophate
- Malathion
- ACh release promoters
- Alpha GPC
- Cisapride
- Droperidol
- Domperidone
- Metoclopramide
- Risperidone
- Paliperidone
- Anti-adrenergics: See also alpha blocker and beta blocker
- Clonidine (α-receptor agonist, α2 > α1, giving negative feedback)
- Methyldopa (α2 agonist, giving negative feedback)
- Propranolol (β-receptor antagonist)
- Metoprolol (β-receptor antagonist)
- Atenolol (β1 antagonist)
- Prazosin (α1 antagonist)
- Oxymetazoline (partial α2 adrenergic agonist)
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