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In the previous lectures we discussed the cholinergic agonists so today we’ll discuss the cholinergic antagonists cholinergic antagonists are those agents that bind to cholinergic receptors muscarinic or nicotinic and prevent the effects of acetylcholine and other cholinergic agonists they are divided into three groups according to their sites of action to clarify
This let’s use that illustration from the autonomic receptors lecture the first group is the ant muscarinic agents which are selective blockers of muscarinic receptors causing the effects of parasympathetic innervation to be interrupted in addition they block the few exceptional sympathetic neurons that are cholinergic such as those innervating the salivary and
Sweat glands they have little or no action at skeletal neuromuscular junctions or autonomic ganglia as they have nicotinic receptors they are also known as anacolinergic agents or parasympathetics and they are the most clinically useful group of the cholinergic antagonists the second group is the ganglionic blockers these agents block the nicotinic receptors of
The sympathetic and parasympathetic ganglia clinically they are the least important of the cholinergic antagonists the third group is the neuromuscular blocking agents mostly nicotinic antagonists they interfere with transmission of efferent impulses to skeletal muscles now let’s discuss the ant muscarinic agents the first one is atropine it binds competitively and
Prevents acetylcholine from binding to muscarinic receptors and this effect can be reversed by using ethically naster ace agent leading to accumulation of acetylcholine and increasing its effect to discuss its actions we have to go back to autonomic receptors lecture where we knew the effects of parasympathetic innervation on each muscarinic receptor then reverse
All we said then as it repeat blocks these receptors now let’s discuss atopine actions uses and its alternative and muscarinic drugs at the same time atropine blocks muscarinic activity in the eye resulting in mitriasis to light and cycloplegia which is the inability to focus for near vision and intraocular pressure may rise especially in patients with closed
Angle glaucoma so it can be used as an ophthalmic solution and it is available with the brand name isoptoatrypine but the problem that it has a very long duration of action for about 7 to 14 days so it has been replaced by shorter acting ophthalmic solutions such as cyclopentylate which has about 24 hours duration of action tropicamide which has about six hours
Duration of action atropine decreases the tone and motility of the gi tract but it does not affect the production of hydrochloric acid significantly so it can’t be used for peptic ulcers but can be used as an antispasmodic drug but it is not the best as the dose used to treat spasms also reduce saliva secretion ocular accommodation and urination so it has been
Replaced by a more selective agent hyacinth butyl bromide it is used as antispasmodic in case of intestinal renal or biliary spasms it is available with the brand name buscopan tablets and injection atropine also causes bronchitisation and decreased bronchial secretions but it has been replaced by agents that are used as inhalation and dose not have any systemic
Effects such as ibutropium and sheotropium which are known commercially as atrovent and spiriva respectively these agents are approved as bronchitis litters for maintenance treatment of bronchospasm associated with chronic obstructive pulmonary disease hypertrophium is also used in the acute management of bronchospasm in asthma shiotropium is administered once
Daily a major advantage over ipretropium which requires dosing up to four times daily atropine causes relaxation of detrizor muscle of urinary bladder causing urine retention so it can be used for overactive bladder but it has been replaced by agents that are selective to muscarinic receptors in the bladder such as deryphanisin faceotarodine oxybutynin saliphanasan
Toltorodine and truspium chloride that are known commercially as enablex tovias ditropan vesicare deutrol and sanctura respectively but they still have some side effects including dry mouth constipation and blurred vision atropine increases the heart rate known as tachycardia so it can be used to treat bradycardia of varying etiologies and it blocks muscarinic
Receptors in the salivary glands producing dryness of the mouth it also decrease secretions of sweat and lacrimal glands inhibition of secretions of sweat glands can elevate body temperature which is dangerous especially in children atropine can also be used as antidote for cholinergic agonists in case of organophosphate insecticides or nerve gases poisoning and
Overdose of clinically used anticlean esterases such as fissostigmine it also can be used in treating central toxic effects of anticlean esterases as it can enter the cns adverse effects of uterpne depend on the dose it may cause dry mouth blurred vision tachycardia urine retention and constipation effects on the cns include restlessness confusion hallucinations
And delirium which may progress to depression collapse of the circulatory and respiratory systems and death low doses of cholinesterase inhibitors such as physostagmine may be used as toxicity other ant muscarinic agents are scopolamine produces effects similar to those of atropine but it has a greater action on the cns and a longer duration of action as compared
To atropine it is one of the most effective anti-motion sickness drugs available and it is available as a topical patch that provides effects for up to three days scopolamine is also used for post-operative nausea and vomiting it also has the unusual effect of blocking short-term memory it produces sedation but at higher doses it can produce excitement it may also
Produce euphoria and is susceptible to abuse ben stirpene and trixofinidal which are known commercially as cogentine and artan respectively they are useful as adjuncts with other anti-parkinsonian agents to treat parkinson’s disease and other types of parkinsonian syndromes including antipsychotic induced extrapyramidal symptoms that’s all for this lecture in the
Upcoming lecture we will discuss the ganglionic blockers and the neuromuscular blockers you can download the pdf of this lecture from the link down in the description subscribe and download medical videos application from google play store follow us on social media to easily get our newest videos you
Transcribed from video
Pharmacology [ANS] 8- Cholinergic Antagonists Part 1 [Atropine – Scopolamine – Benztropine …etc] By Medical Videos [ ANIMATED ]
