Carbachol = cholinomimetic drug that binds and activates the acetylcholine receptor. It is a cholinergic agonist used for treating glaucoma or during ophthalmic surgery. Choline carbamate
Positively charged quaternary ammonium compound
Not well absorbed in GIT tract and does not cross the BBB
Not easily metabolised by cholinesterase
2-5 min onset of action
Duration of action 4-8 hours (topical), 24 hours for intraocular administration Parasympathomimetic that sitmulates both muscarinic and nicotinic receptors
Methacholine = Synthetic choline ester, acts as a non-selective muscarinic receptor agonist in the parasympathetic nervous system. Used to diagnose bronchial hyperreactivity (asthma and chronic pulmonary obstructive disease). Adverse effects – bradycardia and hypotension as it is a cholinomimetic. Little effect on nicotinic receptors
Charged quaternary amine structure – essential for activity Does not cross BBB
Not easily broken down by acetylcholinesterases (broken down at slow rate) however the ester makes it susceptible to AChE
Beta-methyl group – selectivity towards muscarinic receptors compared to nicotinic receptors Benzoylcholine = Strong nicotine-like properties and weak muscarine-like properities. Contains a benzoic ester grouping (like many local anaesthetics) Suxamethonium = nicotinic acetylcholine receptor agonist – induce muscle relaxation and short term paralysis. Depolarising neurmuscular blocker, acting on nicotinic receptors to result in persistent depolarisatin of the motor end plate. It is degraded by butyrylcholinesterase (plasma cholinesterase). Hydrolysis by BchE is much slower than that of ACh by AChE.
Physostigmine: (eserine) parasympathomimetic alkaloid, reversible cholinesterase inhibitor. Acts by interfering with metabolism of ACh. It is a covalent inhibitor (reversible – bond hydrolysed and released) of AChE. It indirectly stimulates both nicotinic and muscarinic acetylcholine receptors. Used to...
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