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,
and brain anti-nicotinic drugs like varenicline.
Let's talk about the ganglionic neurons.
Remember I was telling you that gangs go out and smoke,
so ganglionic neurons are nicotinic.
So these drugs do act at the ganglia.
These were the first of the antihypertensive drugs ever
developed. These drugs are 60, 70, 80 years old.
Hexamethonium is that prototypical agent.
There are others like mecamylamine, 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 two,
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 rain forest,
and it was being used as a paralytic
on the ends of arrows by some native tribesmen.
So that's how we came to know about curare.
We also use drugs that are anti-nicotinic that work
in the brain.
Varenicycline is a partial agonist of nicotine, and it's
very effective in reducing the dependency upon cigarette.
It works about 60 to 70 % of the time when used correctly.
Let's move on to the smooth muscle and neuromuscular neurons.
Now, the smooth muscles neuromuscular neurons are muscarinic.
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? Anti-muscarinic antagonists, the
nonselective 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 anti-muscarinic 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 it's class will act on
that synaptic cleft to cause that effect.
Okay. We also use anti-muscarinic agents in Parkinson's
disease. Benztropine, biperiden, triphenidyl.
These are drugs that we are going to talk about later.
We use scopalamine in motion sickness.
It's available as a pill or patch.
Most people know what a scopalamine patch is.
It's a very effective anti-nauseant.
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 turned 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?
Anti-muscarinic 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.
Atropine is used in "codes" for pulseless electrical activity.
Now, PEA is rarely seen in real world,
clinical practice you'll find that the atropine
doesn't get used very much.
In the lung, anti-cholinergics 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 are 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 secretion and you can't see where you're going with
the intubation instrumentation. 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?
It's an anti-muscarinic agent.
Old treatments for peptic ulcer disease, we no longer use them.
I just mention 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, anti-cholinergic effects,
reduce urgency in mild cystitis and overactive bladder syndrome.
These are the various drugs that we have available.
They are very commonly used in nursing homes.
It's worthwhile knowing these drugs when you get out into
practice. Unfortunately, we use the trade name 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 anti-cholinergics? We call this anticholinergic crisis.
And this is a very old saying, and patient 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 have lost the ability to properly thermoregulate.
They are red as a beet because they have peripheral vasodilation.
And mad as a hatter, they will have psychosis
and very bizzare kind of behaviour.
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 they will show up on the 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.