Chapter 41: Antiemetic & Antinausea Drugs

Welcome to Last Minute Lecture.

This free chapter overview is designed to help students review and understand key concepts.

These summaries supplement not replaced the original textbook and may not be redistributed or resold.

For complete coverage, always consult the official text.

Welcome back to the Deep Dive.

Today we're focusing on just one source, but it's a crucial one, Chapter 41 from Lilly's Pharmacology, all about anti -medic and anti -nausea drugs.

Our mission really is to get a solid, quick understanding of how these drugs work, the main types, and maybe most importantly, some serious safety considerations when treating nausea and vomiting or emesis.

These are incredibly unpleasant for patients, so knowing how to manage them is key.

Absolutely.

And just to make sure we're all on the same page, let's define a few things right off the bat.

Nausea, that's the feeling, right?

The unpleasant sensation.

And emesis, or vomiting, is the actual physical act of expulsion.

Cut it.

Anti -medic drugs are what we use to, well, prevent or relieve those symptoms.

And the control centers for this are in the brain, the camera receptor trigger zone, the CTZ, and the vomiting center, the VC.

Okay, the CTZ and the VC.

So these drugs are essentially targeting those brain centers to stop the signals.

Pretty much.

The vomiting center of the VC is kind of the command post.

It gets signals from the CTZ, which is like a sensor for troublesome chemicals or drugs in the blood.

Makes sense.

But the VC also gets input from other places, too.

Think about the inner, the labyrinth that's crucial for motion sickness.

Then there's the GI tract itself, sending signals if it's irritated.

And even the higher brain centers, the cerebral cortex, can trigger it through things like fear, pain, or even just bad smells.

Wow.

Okay, so signals are coming from all over motion,

toxins, gut irritation, even our thoughts.

How do drugs manage to target such different triggers?

Is there a common link?

There is, yeah.

The link is the neurotransmitters they use to send those signals.

That's what our drugs go after.

It's why we have different classes of anti -medics.

Oh, okay.

So for signals from the inner ear or the VC itself, you're often looking at acetylcholine and ashen histamines, specifically H1 receptors.

Right.

But if the trigger is something like chemotherapy hitting the CTZ or irritating the gut, then dopamine D2 receptors and serotonin 5 -HT3 become the main targets.

Prostaglandins are also involved in gut irritation.

So you need the right tool for the job.

Depending on the pathway.

Exactly.

And often you need more than one tool, combining drugs to block multiple pathways.

And the source really highlights chemotherapy -induced nausea and vomiting, CINV, and postoperative nausea and vomiting, PONV, says they're particularly tough.

They are.

They often cause really severe symptoms.

So the treatment approach tends to be much more aggressive, often involving combinations right from the start.

Okay.

So let's get into that then.

The core idea is blocking those neurotransmitter pathways.

Right.

That's the fundamental principle.

And like we said, combining different classes often works better because you're hitting multiple signals at once.

All right.

Let's walk through the six main categories mentioned.

First up, anticholinergics.

Yep.

The main one here is scopolamine.

You often see it as a patch placed behind the ear.

And how does that work?

It blocks those acetylcholine receptors, specifically the ones receiving signals from the inner ear, the vestibular system.

So it's really good for motion sickness and sometimes used for postoperative nausea too.

Okay.

But there's a big warning sign here.

A crucial one.

Because it's an anticholinergic, it can dilate the pupils.

That means it's absolutely contraindicated if a patient have narrow angle glaucoma.

It could dangerously increase the pressure inside their eye.

Good to know.

Very important.

Okay.

Category two, closely related,

antihistamines.

Right.

Drugs like diamond hydronate, maybe promethazine.

They block H1 histamine receptors.

But interestingly, many of them also have significant anticholinergic effects.

Ah, so they kind of do double duty.

In a way, yeah.

That anticholinergic action helps reduce secretions and spasms, which is useful again, especially for motion sickness.

Okay.

Now category three, antidopaminergics.

Here we see drugs like prochlorparazine, and again, promethazine pops up.

Their main job is blocking dopamine D2 receptors, primarily in the CTZ.

Many also have some calming effects on the central nervous system.

And they're used for more than just envy.

Yeah.

Sometimes for intractable hiccups, believe it or not, or even certain psychotic disorders, they're quite versatile.

But you mentioned promethazine again, and the text flags it as high alert.

Let's pause there.

Why such a specific strong warning for this one drug?

What's the risk?

It's incredibly serious.

And it all comes down to how it's given the route of administration.

If promethazine accidentally gets into an artery, or sometimes even given subcutaneously, or just incorrectly into a vein, what happens?

They can cause severe tissue damage.

Yeah.

We're talking necrosis, blood clots, even gangrene.

There are cases where amputation has been necessary because of improper IV administration.

Wow.

That's terrifying.

So how should it be given?

The safest routes are definitely oral or deep intramuscular injection.

If you must give it IV, it needs extreme care.

Dilute it properly, push it very slowly, and use a large, reliable vein.

Never, ever a small vein in the hand or wrist.

Okay.

Message received.

That's a critical safety point.

Right.

Moving on to category four, prokinetics.

Metoclopramide is the example here.

Yes.

Metoclopramide.

This one has a neat dual action.

How so?

Well, first, like the antidopaminergics, it blocks dopamine in the CTZ.

But second, it actually stimulates helocholine receptors in the GI tract.

And what does stimulating AC and the gut do?

It increases peristalsis, basically.

Yeah.

It gets the stomach moving and helps it empty faster.

So it tackles the nausea centrally and helps with the underlying issue if it's related to slow stomach emptying, like in GERED or diabetic gastroparesis.

It seems very useful.

But there's a catch, especially with long -term use.

There is, unfortunately.

Long -term use, generally considered more than 12 weeks, carries a significant risk of developing tardive dyskinesia.

That's the involuntary movement disorder.

Exactly.

It can be irreversible, and the risk seems higher in older adults, particularly older women.

So it's a serious consideration for chronic therapy.

You have to weigh the benefits against that risk.

Definitely.

OK.

Now for category five, which you mentioned really changed the game for CINV and PONV, the serotonin blockers, or 5 -HD3 blockers.

Ondansetron is the big one.

Ondansetron.

Yes.

Zofran is a common brand name.

This class was revolutionary,

because serotonin is a major player in triggering nausea from chemo and surgery.

How do they work differently?

They specifically block those 5 -HD3 receptors, and they do it in multiple places at once in the GI tract, where chemo often causes irritation, in the CTZ, and in the vomiting center itself.

It's a much more targeted approach for those specific severe types of nausea.

And it's used in pregnancy, too.

Yes.

Ondansetron is often used for hyperemesis gravidarum, which is severe nausea and vomiting during pregnancy, when other measures haven't worked.

Right.

OK.

Last main category.

Tetrahydrocannabinol or THC.

Yeah.

These are pharmaceutical forms, like Bronabinol or Nabloni.

Their mechanism is a bit different, more central.

How do they work?

They seem to have inhibitory effects on pathways involving the reticular formation, the thalamus, and the cerebral cortex.

It's less about blocking a specific trigger signal, and more about altering mood and perception in a way that dampens the whole nausea and vomiting response.

And they have other uses, too.

Yes.

Besides CINV, they're also used to stimulate appetite and help patients gain weight, particularly in conditions like AIDS or advanced cancer, where wasting can be a problem.

Got it.

And the text also briefly mentions a couple of others.

Aprepetent.

Right.

Aprepetent.

It's a neuro -kenin -1 receptor antagonist.

It's not usually used alone, but added on to other drugs,

like Ondansetron and maybe a steroid like dexamethasone, especially for chemo regimens that are known to be highly likely to cause vomiting.

It boosts their effect.

And one specifically for pregnancy?

Yes.

The combination product.

Doxylimus oxtenate, which is an antihistamine, and paradoxin hydrochloride, which is vitamin B6, marketed specifically for nausea and vomiting in pregnancy.

OK.

That covers the arsenal.

Now, let's talk broader clinical issues.

Adverse effects seem pretty common across the board.

They are, largely because many of these drugs aren't perfectly selective.

They hit their target receptor, but might also affect similar receptors elsewhere.

The most common side effect you'll see, especially with the older antihistamines, antidoping meridgics, and anticholinergics, is CNS depression.

Meaning drowsiness?

Drowsiness?

Yeah.

Lethargy.

Dizziness.

Maybe some confusion.

And this leads to a major interaction risk.

Additive CNS depression.

If a patient takes these antiemetics along with alcohol, opioids, benzodiazepines, or other sedating drugs, the effect can be dangerously amplified.

That's a critical counseling point.

What about other interactions?

Well, anticholinergics, combined with other drugs that have anticholinergic properties like some antihistamines or antidepressants, can lead to additive drying effects, dry mouth, urinary retention, constipation.

And a prepadent has some specific interactions.

It can affect warfarin levels, so you need to monitor INR closely, and it might make oral contraceptives less effective.

And going back to that crucial administration safety point, it wasn't just promethazine, right?

There was another drug mentioned with similar risks.

Hydroxazine.

Yeah.

Yes.

Another antihistamine sometimes used for nausea.

The warning is just as stark.

Never give it IV

intraarterially or subcutaneously due to the high risk of severe tissue damage.

Oral or IM only.

The right root mantra is absolutely vital for both promethazine and

Okay.

So putting this all together for nursing practice, the goal is obviously to stop the nausea and vomiting, but also to manage the consequences, right?

Like dehydration.

Exactly.

Preventing or minimizing fluid and electrolyte imbalances and nutritional problems is paramount.

So baseline assessment is key.

What are you looking for?

You need a really good handle on their hydration status.

Check their intake and output.

Look at

mucous membranes.

Capillary refill time should be quick, less than five seconds, ideally.

And baseline labs are essential.

Electrolytes, hemoglobin, hematocrit, give you a picture of their fluid volume and electrolyte balance.

And specific checks, depending on the drug.

Definitely.

If you're giving an anticholinergic or antihistamine, you must check for a history of glaucoma.

If it's an antidopaminergic or metoclopramide, you need to be vigilant for any abnormal movements, those extra pure metal symptoms or EPS, especially if it's longer -term use.

And what about non -prescription things?

The text mentions ginger.

Right.

Zingiber or Ficinal.

People often use it for nausea.

It's generally considered safe, but it might have some mild antiplatelet effects.

So theoretically, there could be an increased risk of bleeding if someone's taking it along with anticoagulants like warfarin.

It's important to ask about all supplements.

Good point.

Okay.

So assessment is done.

What about implementation?

How do we actually use these drugs effectively?

The single most important strategy is prevention.

These drugs work much better if you give them before the nausea starts, rather than trying to chase it once it's established.

So timing is everything, especially with chemo.

Absolutely.

For CINV, you're typically giving the anti -matic, like Ondansetron, about 30 to 60 minutes before the chemotherapy infusion starts.

For Ondansetron specifically, the guideline is often 30 minutes prior.

And what if nausea breaks through anyway?

Do you switch drugs?

Not usually, no.

If nausea persists or breaks through the prophylactic dose, the approach is typically to add another drug from a different class, hitting a different pathway.

You maintain the scheduled doses and use the second drug for breakthrough, or add it to the regular schedule.

It's about multimodal therapy.

Makes sense.

And non -drug approaches.

Oh, definitely important too.

Simple things like avoiding spicy, fatty, or strong -smelling foods, eating small, frequent, bland meals.

Maybe not drinking fluids with meals, but rather between them.

And trying not to lie down flat right after eating can all help.

And patient teaching.

What are the key warnings?

The big ones are drowsiness and potential hypotension, especially orthostatic hypotension, where they feel dizzy standing up.

So warn them about driving or operating machinery,

and reinforce, strongly, avoiding alcohol or other CNS depressants while taking these meds.

Right.

Then evaluation is checking if it worked.

Pretty much.

Are the nausea and vomiting reduced or gone?

Are their fluid and electrolyte levels stable?

And just as importantly, are they experiencing any adverse effects?

Watching for drowsiness, dizziness, those extrapyramidal symptoms, if relevant.

Okay.

So what does this all mean?

It feels like the big picture is understanding these distinct pathways,

ACH1 dopamine serotonin THC effects, and using the right drug, or often drugs, to block them.

And timing, especially prophylactic timing, is crucial.

Plus, that huge safety emphasis on administration route for certain drugs.

You got it.

And there's one more layer, especially with things like chemo, the psychological aspect.

We talked about CNV, but there's also anticipatory nausea and vomiting.

Where the patient feels sick just thinking about the treatment.

Exactly.

They start to associate the clinic, the smells, the whole experience with being sick from previous cycles.

It's a learned response.

This is actually why sometimes an anxiolytic like lorazepam is included in the anti -medic regimen.

Not just for sedation.

Not just for sedation, though that helps.

It's also thought to help blunt the memory of the nausea and the anxiety associated with it, trying to prevent that anticipatory response from developing or getting worse.

It's fascinating how intertwined the physical and psychological are here.

That really is fascinating, treating the memory and expectation almost as much as the physical trigger.

So thinking about that, and the strategy of giving anti -medics before symptoms start, how does that proactive pharmacological approach potentially change a patient's whole experience, their psychological and physical relationship with something difficult like chemotherapy?

What stands out to you?

That gives us a lot to think about.

That wraps up our deep dive into the world of anti -medics, all thanks to chapter 41 of Lily's.

Thank you for providing the source material for this really important clinical discussion.

We'll catch you on the next deep dive.