Anticholinergic Drugs

by Pravin Shukle, MD

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    00:00 Let's move on to anticholinergics. Cholinergic receptor antagonists can be anti-nicotinic and these are ganglion blockers like hexamethonium, neuromuscular junction blockers like curare or tubocurarine. Let's talk about the ganglionic neurons. Remember I was telling you that gangs go out and smoke so gangs, ganglionic neurons, are nicotinic. So these drugs do act at the ganglia. These are the first of the anti-hypertensive drugs ever developed. So these drugs are 60, 70, 80 years old. Hexamethonium is that prototypical agent. There are others like Mecomine, not used anymore and trimethaphan which has some of the derivatives being used in clinical practice today but trimethaphan itself isn't being used. You don't need to know the last 2 but definitely know hexamethonium. What about toxins causing paralysis? I mentioned briefly before about curare. It was found in the deep jungle in the Amazon rainforest and it was being used as a paralytic on the end of arrows by some native tribesman. So that's how we came to know about curare. Let's move on to the smooth muscle and neuromuscular neurons. Now the smooth muscle, neuromuscular neurons, are muscarinic.

    01:29 The other types of end organs are sweat glands which are also muscarinic. How do I remember that? Musky smell means sweat and muscles. So that's how I tend to remember that smooth muscle and neuromuscular neurons are muscarinic. What are these antagonists? Antimuscarinic antagonists, the non-selective one is atropine. I already told you that it is used as an antidote in sarin gas exposure. It's also used in cardiac codes. The M1 selective antimuscarinic drug is pirenzepine. Now drugs ending in oxime like pralidoxime are cholinesterase regenerators. We spoke before about cholinesterase inhibitors. This is where the double negative comes in in the central nervous system. A cholinesterase inhibitor inhibits the enzyme that breaks down acetylcholine. So a cholinesterase inhibitor increases the amount of acetylcholine. A cholinesterase regenerator increases cholinesterase so you reduce the amount of acetylcholine in the synaptic cleft. So pralidoxime and other drugs in its class will act on that synaptic cleft to cause that effect. Okay, we also use antimuscarinic agents in Parkinson's disease. Benztropine, biperiden, triphenidyl these are drugs that we're going to talk about later. We used scopolamine in motion sickness. It's available as a peel or patch. Most people know what a scopolamine patch is. It's a very effective antinauseant.

    03:26 And one other thing that I think you need to remember for when you're on the wards is benztropine. Benztropine is an antidote to acute dystonia where people are contracted and unable to move and they often will have their head turn to one side as far as it will go. So benztropine is an antidote to that. We're going to cover that in a later lecture as well. What are the effects on the eye? Antimuscarinic agents cause dilation. Okay. Atropine acts over 72 hours, homatropine acts over 24 hours, and this one acts over 30 minutes. Now atropine is derived from the belladonna plant which I have illustrated here. It's a tertiary amine, it's lipid soluble, it does cross the blood-brain barrier and it's duration of action is around 4 hours.

    04:25 Atropine is used in codes for pulseless electrical activity. Now PEA is rarely seen in real-world clinical practice so you find that the atropine doesn't get used very much. In the lung, anticholinergics cause mild bronchodilation. So the prototypical drug for the lung is ipratropium, it's also known as Atrovent. So Atrovent is the green inhaler. The new bronchodilators like tiotropium are also available and are really making a huge impact on respiratory therapy. We're going to be talking about that in our respiratory pharmacology lecture. There is also a mild reduction in airway secretions. Atropine can sometimes be used as a direct agent when you're trying to intubate somebody and they have tons of mucus secretions that you can't see where you're goiong with the intubation instrumentation. We've also used and I've also used it personally when I'm doing bronchoscopies because it does reduce airway secretion. Okay, what about the effect on the gut as an antimuscarinic agent? Old treatments for peptic ulcer disease we no longer use them. I just mentioned them here for your own interest, it is not going to be on an exam and it's not a big part of our thought processes anymore. In terms of the urinary tract, anticholinergic effects reduce urgency and mild cystitis and overactive bladder syndrome. These are the various drugs that we have available. They're very commonly used in nursing homes. It's worthwhile knowing these drugs when you get out into practice. Unfortunately, we used the trade names so much that the generic names kind of fallen by the wayside and it's because they sound so much like they would relieve urinary symptoms, and they are listed here. Okay, what about toxicity? So what happens if you take too many anticholinergics? We call this anticholinergic crisis and this is a very old saying and patients are dry as a bone, hot as a pistol, red as a beet, and mad as a hatter. So patients who are dry have what we call atropine fever. They are very dry, they are very warm, they've lost the ability to properly thermoregulate. They're red as a beet because they have peripheral vasodilation and mad as a hatter they will have psychosis and very bizarre kind of behavior. Treat anticholinergic toxicity with physostigmine. That is the antidote for that type of toxicity. Well, there you have it. We did a very difficult topic. I think you guys are great to have lasted until the end of this lecture. This is the kind of stuff that does show up on exams. So if you want to watch this lecture again I do encourage it. I found it difficult when I was studying so I tried to make it as easy as possible and we do have some questions for you so I encourage you to do practice questions in this so that when you get to your exam you'll nail it. Thank you very much.

    About the Lecture

    The lecture Anticholinergic Drugs by Pravin Shukle, MD is from the course ANS - Pharmacology.

    Included Quiz Questions

    1. Nicotinic cholinergic.
    2. Muscarinic cholinergic.
    3. Nicotinic adrenergic.
    4. Muscarinic adrenergic.
    1. Nicotinic cholinergic antagonist.
    2. Dopamine receptors antagonist.
    3. Nicotinic muscarinic agonist.
    4. Nicotinic cholinergic agonist.
    5. Serotonin agonist.
    1. Probably a nicotinic receptor blocker.
    2. Probably an adrenergic agonist.
    3. Probably an adrenergic blocker.
    4. Probably a calcium channel blocker.
    1. Muscarinic cholinergic blocker
    2. Nicotinic cholinergic blocker.
    3. Adrenergic blocker.
    4. Calcium channel blocker.
    1. ...has developed an acute dystonia due to a drug reaction. The antidote is benztropine, a central anticholingergic agent.
    2. ...has developed an acute dystonia due to a drug reaction. The antidote is bisoprolol, a central anticholingergic agent.
    3. ...has developed an acute dystonia due to a drug reaction. The antidote is biguanide, a central anticholingergic agent.
    4. ...has developed an acute dystonia due to a drug reaction. The antidote is betamethasone, a central anticholingergic agent.
    1. ...increased erectile function in patients with erectile dysfunction.
    2. ...decreased airway secretions.
    3. ...dry mouth.
    4. ...pupillary mydriasis.
    1. ...anticholinergic toxicity; he was probably exposed to toxic levels of a chemical on the farm. The antidote is physostygmine.
    2. ...anticholinergic toxicity; he was probably exposed to toxic levels of a chemical on the farm. The antidote is benztropine.
    3. ...adrenergic toxicity; he was probably exposed to toxic levels of a chemical on the farm. The antidote is benztropine.
    4. ...neurotoxicity; he was probably exposed to toxic levels of a chemical on the farm. The antidote is bisoprolol.

    Author of lecture Anticholinergic Drugs

     Pravin Shukle, MD

    Pravin Shukle, MD

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    Concisely structured.
    By PRATHAM N. on 26. December 2017 for Anticholinergic Drugs

    Just what is needed for the clinics and exam Bare minimum leads to better retention and the results.