Cholinergic drugs are parasympathomimetics or cholinomimetics because they mimics the PSN system or they mimics the Ach activity.These are classified into two wide groups.
Some drugs acts just similar to the normal Ach and other drugs just decreases the metablism of Ach so that Ach can act for long time and hence cholinergic activity is maintained.
A) Cholinergic agonist-
These drugs perform similar action as of Ach that’s why they are called as Cholinergic agonist.They are of two types.
1)Choline esters-
•Acetyl choline
•Methacholine– Used in supraventricular tachycardia
•Bethanecol – Used in overflow incontinence due to Diabetic neuropathy.When the nerve innervating the bladder are affected due to DM then the Detrussor muscles are unable to contract and internal sphincter are unable to relax then this type of drug is used which acts on its receptor and contracts the bladder which finely helps in emptying the bladder
•Carbachol
2)Alkaloids –
These drugs are taken from plant/animal sources.
•Pilocarpine– When given orally then used in sjogren syndrome,it is an autoimmune disorder where salivary glands are damaged causing xerostomia and other symptoms so,as we know that ach is prosecretory so it increases the salivary secretion and hence treated xerostomia related problem.
When Pilocarpine given as eye drop then it may be used in galaucoma, iridocyclitis
[In iridocyclitis we use Pilocarpine which causes misosis and we use Phenylepherine (adrenergic drug) which causes mydriasis]
•Muscarine
B) Anti Cholinesterase Drugs-
These drugs acts on the cholinesterase enzyme and stops it activity so that less Ach is metabolised which increases the activity of Ach on its receptors.
They are of two types based on its activity.
1)Reversible anti cholinesterase drugs-
These drugs acts reversibly i.e they stops the metabolism of Ach and increases its activity.These drugs stops cholinesterase for 30 minutes.And then afterwards Ach is metabolised and removed from its receptors.
•Physostigmine– It is used in Belladona poisoning. When Atropa Belladona is miss-used by someone then it causes all the effects of anti Cholinergic i.e it causes decreases ach activity and to neutralize/stop its effects we use Physostigmine which causes increased activity of Ach on receptors and hence treats Belladona poisoning.
Also it is used in Galaucoma,where IOP of eye is increased.
•Neostigmine– Used in Myesthenia gravis,in snake bite
Because neostigmine mainly have action on nicotinic receptors.so anti snake venom + neostigmine is given.
•Pyridostigmine
•Tacrine
2)Irreversible anti cholinesterase drugs-
They irreversibly increases the action of Ach on its receptors by anti cholinesterase activity.
•Organophosphorus compounds– They are basically used in insecticides, pesticides used by farmers in their land for agricultural purposes.But some time they consume them as an attempt to suicide.So,in this organophosphate poisoning case we use Atropine(Anticholinergic activity on muscarinic receptor) + Pralidoxime (Anticholinergic activity on nicotinic receptor).
Details about Organophosphate poisoning is already discussed in our previous post,you can read it from their itself.
Some centrally acting Anticholinergic drugs:-
•Tacrine
•Donepezil
•Rivastigmine
•Golantamine
As they are centrally acting drug so they may be used in Alzheimer disease.
(In Alzheimer disease Acetycholine levels decreases and Glutamate levels decreases.Also memantine is the other drug which can be used in Alzheimer because memantine increases the glutamate activity)
Uses of cholinergic drugs:- (Summary)
•Methacholine in supraventricular tachycardia
•Donepezil in dimentia
•Pilocarpine in sjogren syndrome(oral), glaucoma & iridocyclitis (eye drop)
•Neostigmine in Myesthenia gravis, snake venom
•Bethanecol in overflow incontinence with DM
•Physostigmine in glaucoma, belladonna poisoning
Contributor- Medico Anant Singh Nanda