Chapter 21: Cholinergic Drugs – The Parasympathetic System

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Welcome back to the Deep Dive.

Today, we're really getting into the weeds with some pharmacology.

We're tackling Chapter 21 from Lilly's Pharmacology, cholinergic drugs.

You might know them as parasympathomimetics.

That's right.

Our goal here is pretty straightforward.

A rapid but thorough assimilation.

We want you to walk away really understanding the drug classes, how they work, their uses, the risks, and those absolutely critical nursing points.

Yeah, cutting through the noise.

Exactly.

So let's start with the basics.

What system are we even talking about influencing here?

Okay.

So fundamentally, we're talking about the parasympathetic nervous system, the rest and digest system.

Exactly.

It's the counterpart to the fight or flight sympathetic system.

It's all about maintaining homeostasis when things are calm.

Like slowing the heart rate.

Slowing the heart rate, increase in digestion,

promoting secretions, constricting the pupils, it's called meiosis, basically keeping the body running smoothly during downtime.

And the main chemical messenger driving all this?

That would be acetylcholine, SA.

It's the key neurotransmitter for the PNS.

But just having the messenger isn't enough, right?

You need a way to turn it off.

Precisely.

And that's where acetylcholinesterase or SCE comes in.

The enzyme.

The enzyme that breaks down SCE.

So cholinergic pharmacology, really it's all about manipulating that balance between S signaling and ACE cleanup.

Okay.

Let's unpack this then.

If AC is the key, where are the locks?

What are the receptors?

Good question.

There are two main types of cholinergic receptors we need to know.

They're actually named after substances, alkaloids that stimulate them.

Okay.

Which one should we start with?

Let's talk nicotinic receptors first.

Nicotinic.

Okay.

Now these are interesting because they're located in the ganglia, those nerve junctions in both the sympathetic and parasympathetic systems.

Oh, right.

So stimulating these could have pretty widespread effects.

Potentially, yes.

And they're stimulated by, well, nicotine, as the name suggests.

And the other type.

The one more specific to the parasympathetic effects we often want.

Those are muscarinic receptors.

Muscarinic.

These are found postsynaptically, right on the target organs, smooth muscle, glands, the heart muscle, the places directly innervated by parasympathetic fibers.

And stimulated by muscarin.

Got it.

So when AC or one of these drugs we're discussing

binds to either receptor type, what actually happens at the cell level?

Well, the binding changes the cell membrane's permeability.

Ah, opens the gate, so to speak.

Sort of, yeah.

It allows calcium and sodium ions to flow into the cell.

Okay.

That influx of positive ions depolarizes the cell membrane.

And that electrical change, that depolarization, is what stimulates the organ to do its job, contract, secrete, whatever it is.

Right.

So now we know the target system and the receptors.

How do the drugs actually achieve this stimulation?

You mentioned manipulating the balance.

Exactly.

There are two main strategies, two classes of cholinergic drugs.

Okay.

First, you have the direct acting agonists.

Think of these as mimics.

Like botanical, polycarpene.

Precisely.

They bind directly to the cholinergic receptor, muscarinic or nicotinic, and activate it, just like SCH itself would.

Simple enough.

What's the second strategy?

The second group uses a different approach.

They are the indirect acting agonists.

Also called cholinesterase inhibitors?

Yes.

That's probably the more common name.

And it tells you exactly what they do.

They inhibit the enzyme, ACE.

Right.

Drugs like dunpeazole, physostigmine, pure dostigmine.

They block ACE from breaking down the naturally occurring 8.

So you end up with more ACE hanging around in the synapse, available to stimulate the receptors for longer.

Exactly.

It's like preventing the cleanup crew from doing its job so the signal keeps going.

And within those inhibitors, there's another distinction, right?

Reversible versus irreversible.

Yes.

And it's a critical difference.

Reversible inhibitors like dunpeazole or curatostigmine bind to ACE only temporarily.

Their effects wear off.

Right.

Irreversible inhibitors, though, things like certain pesticides,

organophosphates, they form a long -lasting, essentially permanent bond with ACE.

Wow.

So the body has to make entirely new enzyme molecules.

That's right.

It takes time, which is why they're so dangerous.

This really highlights something important.

The difference between hitting the right receptors at the right dose and going too far.

Absolutely critical.

At the recommended therapeutic doses,

these drugs mostly stimulate the musterinic receptors.

That's where we get the desired rest and digest effects.

The therapeutic benefits.

Yes.

But if the dose is too high or in cases of toxicity, you start hitting those nicotinic receptors too.

And that's where the trouble starts.

That's where you see the more severe, often undesirable, and sometimes dangerous adverse effects.

It's all about dose and receptor selectivity.

Okay.

Let's pivot to where we actually use these drugs clinically.

You mentioned they primarily target the GI tract, the bladder, and the eyes.

Those are definitely key areas.

Let's look at the direct acting ones first.

Botanical brand name urecholine is a classic example.

What's it used for?

It's given orally, usually to treat ectin A basically, lack of muscle tone in the bladder or the GI tract, often used after surgery when things slow down.

So it helps wake up the muscles.

Yeah, it increases muscle tone and motility, gets things moving, and it also relaxes the outlet sphincters in the bladder and GI tract, which helps with emptying.

Makes sense.

And then they're the topical ones for the eyes.

Right.

Pylacarpine and carbacol, usually as eye drops.

For glaucoma.

Primarily, yes.

They cause meiosis pupil constriction.

Okay.

That constriction helps open up the drainage channels in the eye, allowing the aqueous humor to drain better, which lowers the intraocular pressure, which is the goal in glaucoma.

And Pylacarpine also comes in tablets.

It does.

Yeah.

Taken orally, it's used to treat xerostomia, which is excessively dry mouth.

It stimulates saliva production.

Interesting.

Okay.

Now shifting to the indirect agents,

the cholinesterase inhibitors.

Yeah.

Where do they shine?

A major use is in myasthenia or MG.

That's the autoimmune disease affecting muscle strength, right?

Exactly.

There's a problem with a transmission at the neuromuscular junction.

So drugs like pyridostigmine, that's the main one for treatment work by increasing the amount of ASHA available at those junctions.

Boosting the signal to improve muscle strength?

Precisely.

We also use a short acting one, edrophonium, mainly for diagnosis.

It helps figure out if someone has MG or sometimes differentiate between a worsening MG and a cholinergic crisis, which we'll talk about.

Got it.

And these inhibitors are also antidotes.

Yes.

Phisostigmine is a key antidote.

It's used for poisoning with anti -cholinergic drugs, drugs that block HE.

So it counteracts the blockage.

Right.

And it's also used for poisoning by those irreversible cholinesterase inhibitors we mentioned, like organophosphate pesticides.

Okay.

Kind of fighting fire with fire in a controlled way.

You could say that, but perhaps the most common use you'll encounter, especially in long -term care, is for Alzheimer's disease.

Right.

Drugs like dunpeazle, rivastigmine, galantamine.

Yes.

The thinking here is that in Alzheimer's, there's a decline in HE levels in certain parts of the brain involved in memory and learning.

So these drugs boost the HE -H levels that are left.

They do.

They aim to enhance or maintain cognitive function.

But here's the really crucial point, something every and student needs to communicate clearly.

They aren't a cure.

They absolutely are not a cure.

They don't stop the disease progression.

They don't reverse it.

They offer symptomatic improvement.

And honestly, the benefit is often modest.

And not everyone responds, right?

The text mentioned may be 15, 30%.

Exactly.

And it can take up to six weeks to even see if there is any benefit.

Managing expectations for patients and families is absolutely vital.

Before we dive into the risks, there's that one other Alzheimer's drug that often gets mentioned alongside these, but isn't actually cholinergic.

Ah, you mean Mementine.

Yes.

Right.

Important distinction.

Mementine is used for moderate to severe Alzheimer's, but it works totally differently.

It's an NMDA receptor antagonist.

So a different pathway altogether.

Completely different mechanism.

Targeting glutamate pathways thought to be overactive in AD.

Good to know, but not part of this class.

Okay.

Good clarification.

Now let's talk safety.

Since these drugs ramp up the rest and digest system, when should we absolutely not use them?

What are the big contraindications?

Given the widespread effects, the list is pretty significant.

Obviously known drug allergy, any kind of mechanical obstruction in the GI or urinary tract is a no go because stimulating motility against a blockage is dangerous.

Right.

Could cause a perforation.

Exactly.

Also significant bradycardia, very low blood pressure or known defects in cardiac conduction.

These drugs slow the heart, so you don't want to worsen that.

And respiratory issues.

Big ones.

Because they increase bronchial secretions and can cause bronchospasm, they're contraindicated in conditions like COPD or active asthma.

Okay.

That makes sense.

And the side effects or adverse effects are basically just the desired effects going too far.

Pretty much.

They're extensions of the parasympathetic stimulation.

Think about the systems involved.

Cardiovascular.

Bradycardia, hypotension, which can lead to fainting or syncope and potential conduction issues.

GI tract.

Cramps, increased secretions, nausea, vomiting, diarrhea, everything gets hyperactive.

Respiratory.

Increased bronchial secretions, potential bronchospasms.

That's why the contraindication and asthma COPD is so important.

And other things like eyes, sweat.

Yep.

Lacrimation, tearing, sweating, increased salivation and that pupil constriction meiosis.

Okay.

So those are the expected dose -related side effects.

But what happens if someone gets way too much?

The overdose situation.

That's when we enter the danger zone.

Cholinergic crisis.

Sounds serious.

It is.

It's a life -threatening emergency caused by excessive cholinergic stimulation, usually from an overdose or poisoning.

It can rapidly lead to circulatory collapse,

respiratory failure, shock, and cardiac arrest.

We need to recognize the early signs.

Is there a mnemonic for that?

There is.

And it's crucial to remember S -L -U -D -G -E.

S -L -U -D -G -E.

Okay.

What does that stand for?

Salivation, lacrimation, tearing, urinary incontinence, diarrhea, gastrointestinal cramps, and emesis, vomiting.

S -L -U -D -G -E.

Got it.

So seeing those signs, especially together.

That's your red flag.

Early recognition, seeing flushing, sweating, nausea, those cramps is key to intervening before it progresses to respiratory compromise or cardiovascular collapse.

And if it hits,

if you suspect a cholinergic crisis, what's the immediate action?

What's the antidote?

The number one thing, the specific antidote you must have readily available whenever you're dealing with these drugs is atropine sulfate.

Atropine.

Because it's a cholinergic antagonist.

Exactly.

It directly blocks the effects of the excess A .C., or cholinergic drug, at the muscarinic receptors.

It reverses the crisis.

Does anything else help?

In severe cases, especially with significant cardiovascular problems or bronchoconstriction, epinephrine might also be needed to support blood pressure and open the airways.

But atropine is the primary antidote.

All right.

Let's bring this home for the nursing students and practitioners listening.

What are the absolute must -do nursing considerations?

Let's start with assessment.

Okay.

Baseline assessment is critical.

You absolutely need baseline vital signs.

Pay special attention to blood pressure, both sitting and standing, if possible.

Why specifically VP?

Because of that risk of orthostatic hypotension we mentioned.

These drugs can cause dizziness and increase the risk of falls, especially in older adults.

Right.

What else for assessment?

Particularly for the Alzheimer's drugs.

For drugs like Dunpeazle, you need a good baseline neurological assessment.

What's their cognitive function before starting the drug?

Memory, alertness, orientation.

And tracking progress.

Super important.

Encourage the patient, or more often their family or caregivers, to keep a detailed journal.

Track symptoms, any side effects, mood, cognitive changes.

It really helps gauge the response, especially since it can take weeks.

Okay.

Moving to implementation.

Giving the meds.

Is there anything special about timing, especially for myasthenia gravis?

Yes.

Absolutely crucial for MG patients.

Give their oral cholinergic inhibitors, like pyridostigmine, about 30 minutes before meals.

30 minutes before.

Why?

Because that allows the drug to start working and peak around the time they need the muscle strength for chewing and swallowing.

It significantly reduces dysphagia difficulty swallowing and helps them eat better.

Makes a huge difference to quality of life.

What about for post -op patients getting something like botanical?

Before jumping to the drug for urinary retention or slow gut motility, always make sure non -pharmacological measures have been tried or encouraged.

Like getting them up and walking.

Exactly.

Ambulation, increasing fluid intake, ensuring adequate fiber.

These should always be part of the plan.

The drug is an adjunct, not usually the first line right after surgery.

Good point.

And the big safety net.

Always, always, always ensure that atropine sulfate is readily available in the clinical setting whenever you're administering cholinergic agonists.

You need that antidote close by, just in case.

Okay.

What about long -term care and patient teaching, especially around those Alzheimer's Honesty and safety are paramount.

You have to gently but clearly communicate that these drugs manage symptoms.

They don't cure the disease.

Setting realistic expectations again.

Yes.

And remind them it can take up to six weeks to see effects.

Then safety focus.

That orthostatic hypotension risk is real.

Teach patients to change positions slowly.

Like dangling their feet before standing up.

Exactly.

Go from lying down to sitting for a minute, then sitting to standing.

Slow,

gradual movements to prevent dizziness and falls.

And we shouldn't forget non -drug approaches, right?

The source mentioned exercise.

Yes.

It's important to remember the whole picture.

There was a study mentioned showing that regular physical exercise, like a 12 -week program, actually improved memory and brain function in older adults who had mild cognitive impairment.

So it's not just about the pills?

Never just about the pills.

Medication needs to be integrated with supportive care, good nutrition, social interaction, and yes, physical activity were possible.

Okay.

Great perspective.

So let's try to boil this all down.

If you remember just four things from this deep dive into cholinergic drugs, what should they be?

All right.

Four key takeaways.

First,

cholinergic drugs mimic acetylcholine, ACH, and stimulate the rest and digest or parasympathetic nervous system.

Second, the two main classes are direct acting agonists, which bind directly to the receptors.

And indirect acting agonists, the cholinesterase inhibitors, which block the enzyme ACE, increasing natural ACE levels.

Third,

therapeutic uses are diverse from treating bladder or GI atony and glaucoma to managing symptoms of myasthenia gravis and Alzheimer's disease.

And fourth,

and critically important,

overdose leads to cholinergic crisis marked by SLDGE symptoms and requires immediate treatment with the antidote atropine sulfate.

Perfect recap.

Before we wrap up, any final thought for our listeners to chew on based on this chapter?

Well, looking particularly at the Alzheimer's drugs like Dunpeazle, this chapter really highlights how much of current pharmacology for chronic neurodegenerative diseases is focused on managing symptoms rather than achieving a cure or significantly altering the disease course.

Right.

So the provocative question for you as current or future healthcare professionals is this.

How do we effectively balance this often aggressive pursuit of drug therapy, which may offer modest benefits with the equally vital evidence -based non -pharmacological interventions?

Things like consistent exercise, strong social support, cognitive engagement.

How do we ensure those get the attention and resources they deserve alongside the medication?

That is indeed a crucial question for clinical practice in healthcare systems.

Definitely something to keep thinking about.

Thank you so much for breaking all that down for us.

My pleasure.

And thank you all for joining us for this deep dive into the source material.

We hope this last -minute lecture -style breakdown helps solidify this complex topic.

We'll catch you on the next one.