Chapter 52: Antiemetic and Antinausea Drugs

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Welcome to the Deep Dive.

Today, we're tackling a really critical area from pharmacology, anti -medic and anti -nausea drugs.

Mastering these is, well, essential.

Absolutely, because uncontrolled nausea and vomiting, it's not just unpleasant, it can lead to serious issues.

Right, things like dehydration, electrolyte problems,

even nutritional decline,

big complications.

Exactly.

So maybe first, let's just quickly define our terms.

Nausea, that's the feeling, the urge.

An apophil sensation.

And emesis or vomiting, that's the actual physical act, the expulsion.

Got it.

And anti -medics are the drugs we use to stop or relieve that.

Precisely.

So our mission today for you, our learner, is to give you a clear, quick guide.

We'll walk through the seven main drug classes from the source material, how they work, and crucially, the nursing safety points you absolutely need to know.

Okay, so where do we start?

We need to understand the underlying process first.

How does the body even decide to vomit?

Yeah, let's talk about the brain's control panel for this.

Okay.

So there are two main areas we need to focus on in the brain.

You've got the vomiting center or VC.

Right.

And the cam receptor trigger zone, the CTZ.

VC and CTZ.

So the VC is the one that actually makes it happen.

Yes.

The VC, which is in the medulla, coordinates the whole physical event of vomiting.

It sends out the signals to the muscles.

Okay.

So what's the CPZ's role then?

The CTZ is like the lookout.

It's positioned cleverly sort of outside the main barrier protection,

which means it's really sensitive to chemicals or drugs floating around in the blood.

Think chemotherapy drugs, toxins, that kind of stuff.

So it detects the bad stuff.

Exactly.

And when it does, it sends an alert signal straight to the VC, tells it, hey, something's wrong, initiate vomiting.

Okay.

But it's not just the CTZ sending signals, right?

I remember reading the VC gets input from other places too.

That's right.

It's complex.

Signals come directly from the GI tract, like if there's irritation.

Make sense.

From the cerebral cortex, that's where things like stress, anxiety, or even just the thought of vomiting can trigger it.

Oh, the anticipatory nausea.

And also from the labyrinth in the inner ear.

That's the key one for balance and motion sickness.

So multiple pathways leading to the VC.

Exactly.

And this is crucial for understanding the drugs because those signals aren't just electrical.

They use chemical messengers, neurotransmitters.

Ah, here we go.

The targets for the drugs.

Precisely.

The key players that animatics often block are acetylcholine, or AC.

Okay.

Dopamine, specifically the D2 receptor type.

D2.

Histamine, the H1 receptor.

And serotonin, the 5 -HD3 receptor.

Plus another important one, substance P, which acts on neurokinin 1 receptors.

So AC, E8, D2, H1, 5 -HD3, and neurokinin 1, those are our targets.

Those are the main ones, yes.

Animatics work by blocking one or sometimes more of these pathways.

Which actually leads to an important point, doesn't it?

Since there are multiple routes in, just blocking one might not always be enough.

Exactly right.

Especially for really tough cases like chemo -induced nausea.

That's why you often see different classes of animatics used together to block multiple signal routes.

The combination approach makes sense.

So shall we walk through the seven main classes and see how they hit these targets?

Let's do it.

Starting with the ones that target that inner ear pathway you mentioned for motion sickness.

Perfect.

First up, anti -cholinergics.

The classic example here is scopolamine.

Scopolamine, right.

How does it work?

It blocks those acetylcholine, the ACA receptors, specifically in the vestibular nuclei.

Remember the labyrinth?

Scopolamine stops those motion signals from the labyrinth getting through to the CTZ and VC.

So it directly interrupts the motion sickness signal.

Exactly.

It also has some side effects like drying up GI secretions and reducing muscle spasms, which can sometimes be helpful.

And its main use is clearly motion sickness prevention.

That transdermal patch is pretty common, right?

Yes.

The transdermal patch is key.

You put it behind the ear, usually on a clean, dry, hairless spot.

It lasts about 72 hours.

And the timing?

You need to apply it at least four hours before you expect the motion, like before travel.

Give it time to absorb and work.

Okay.

Crucial safety point with these.

Absolutely critical.

Do not use anticholinergics like scopolamine in patients with narrow angle glaucoma.

It can increase eye pressure.

Big contraindication.

Got it.

Must check for glaucoma.

Okay.

What's next?

Similar mechanism.

Very similar.

Yes.

Class two, antihistamines, the H1 blockers.

Think meklazine.

Meklazine, often used for dizziness too.

Right.

They work much like the anticholinergics by inhibiting those vestibular signals from the inner ear.

They also have pretty strong anticholinergic effects themselves.

So also good for motion sickness and, as you said, vertigo or severe dizziness?

Exactly.

Okay.

So those two handle the motion ear pathway.

What about drugs targeting the central triggers more, like the CTZ?

Now we move to the antidopaminergics.

Key examples are prochlorperazine and, very importantly, promethazine.

Promethazine.

I know that one comes with some serious warnings.

It certainly does.

But first, the mechanism.

They block dopamine, those D2 receptors, primarily in the CPZ.

So they stop those chemical bad stuff signals from getting processed.

Correct.

They're quite versatile, used for general nausea and vomiting, sometimes for psychotic issues, even for stubborn hiccups.

Hiccups.

Interesting.

But you mentioned warnings, especially with promethazine.

Yes.

Because they block dopamine, there's a risk of extrapyramidal symptoms, EPS, those movement -related side effects.

Like tremors or stiffness.

Exactly.

But the really urgent safety alert concerns promethazine administration, specifically IV.

Okay.

This sounds important.

It is.

5e -promethazine carries a significant risk if it accidentally gets injected into an artery instead of a vein.

Oh, no.

It can cause severe tissue damage, necrosis, even leading to amputation in the worst cases.

It's a huge deal.

Wow.

So how should it be given IV then, if it has to be?

The guidance is extremely specific.

It must be diluted, usually in at least 10 milliliters of fluid.

Okay.

Dilute it well.

And it should be given through a large patterned free -flowing 5e line.

Ideally, use the port that's farthest from the patient's actual vein insertion site.

Farthest away.

Or use a large bore vein, like in the forearm.

Absolutely avoid small veins in the hand or wrist.

Right.

Minimize that risk of arterial injection.

This needs careful attention every single time.

Every single time.

And related to this, there's another drug,

The warning there is, never give it IV,

interaterially or subcutaneously.

High risk of tissue damage, too.

Got it.

Hydroxazine, no IV, SC, or interarterial.

Promethazine, extreme caution with IV.

Okay.

Moving on.

Let's talk about a newer class.

The neurokinin blockers.

Example.

A prepotent.

A prepotent.

How does this one work?

It's different, right?

Yes.

It targets substance P by blocking its receptor, the neurokinin 1 receptor, in the substance P in neurokinin 1.

And what's really interesting is how it's used.

It's almost always part of combination therapy.

Ah, back to that multi -pathway approach.

Exactly.

A prepotent is typically given with serotonin blockers and glucocorticoids, specifically to manage chemotherapy -induced nausea and vomiting both the immediate and the delayed types.

It boosts their effectiveness.

So it augments the other drugs.

Important interactions to know.

Definitely.

A prepotent can speed up the metabolism of warfarin.

Oh, so you'd need to monitor INR closely if a patient is on both.

Absolutely.

And it can also make oral contraceptives less effective.

That's a key patient teaching point.

Good to know.

Okay.

Next class.

Prokinetics.

The main drug here is metocloformide.

Metocloformide.

I know this one has a dual action.

It does.

It's quite clever.

First, it blocks dopamine in the CTZ like the anti -dopaminergics we discussed.

Okay.

CPZ action.

But it also directly stimulates peristalsis in the GI tract.

It helps get the stomach moving, pushes contents forward.

So it helps with delayed gastric emptying, GERD.

Exactly.

And also nausea and vomiting, especially related to chemo or radiation.

But being a dopamine blocker, does it carry similar risks?

Yes.

And this is a significant one.

There's an FDA advisory about metocloformide and the risk of developing tardive dyskinesia, especially with long -term use.

Tardive dyskinesia, those involuntary repetitive movements.

Yeah.

And it can be permanent.

It can be, yes.

Which means we really need to question and limit long -term use whenever possible.

A serious consideration.

Okay.

Class number six.

This is a big one, right?

Yeah.

A very big one.

The serotonin blockers, the 5 -HT3 antagonists.

Yeah.

Most well -known is probably Ondansetron.

Ondansetron.

Zofran.

Changed the game for chemo patients, didn't it?

It really did.

Its power comes from blocking those 5 -HT3 receptors effectively.

And crucially, it blocks them in multiple locations.

Where exactly?

When the CTZ and the VC in the brain, yes.

But also importantly, peripherally, in the GI tract itself.

Ah.

So it tackles the signals right where chemo often causes irritation in the gut.

Precisely.

That's why it's so effective for chemotherapy -induced nausea and vomiting,

CINV, and also for preventing nausea after surgery.

And timing is key for CINV.

Absolutely critical.

Ondansetron needs to be given before the chemotherapy starts, usually 30 to 60 minutes prior.

You need the receptors blocked when the chemo hits.

Prophylaxic use.

Got it.

Safety concerns.

Yes.

There are warnings about the potential risk for cardiac dysrhythmias.

Specifically, it can prolong the QT interval on an ECG.

So caution in patients with heart issues or electrolyte imbalances that might predispose them to QT prolongation.

Exactly.

Requires monitoring.

Okay.

And the final class.

Number seven.

Tetrahydrocannabinoids, or THC, derivatives.

Like dronabinol.

Dronabinol -synthetic THC.

How does it work for nausea?

Its anti -medic effect seems to come from inhibitory actions on higher brain centers, the reticular formation, thalamus, cerebral cortex.

It alters mood and perception, which seems to help reduce nausea.

Is it a first line choice?

Usually not.

It's typically considered second line for CINV if other agents haven't worked well.

But it has another useful effect, doesn't it?

Yes, a major one.

It stimulates appetite and can help with weight gain, which is incredibly valuable for patients with AIDS or cancer who are experiencing wasting.

A dual benefit there.

Okay, that covers the seven classes.

Before we get to the nursing process, any other key safety points or specific agents we should highlight?

Yes, a couple of important ones.

First, regarding pediatric poisoning.

A major shift in advice.

Oh, you mean syrup of Ipacac.

Exactly.

The American Academy of Pediatrics has strongly advised against using syrup of Ipacac at home to induce vomiting since way back in 2003.

So telling parents to keep it on hand is outdated advice.

What should they do instead?

Call the National Poison Control Hotline immediately.

That's the standard of care now.

Get expert advice fast.

Okay, critical teaching point for caregivers.

What else?

There's a miscellaneous agent often used for milder nausea like morning sickness, phosphorated carbohydrate solution, brand name Emitrol.

Emitrol?

How does that work?

It seems to act directly on the GI wall locally, reducing smooth muscle contraction or cramping.

So, okay, for mild stuff, but probably not potent enough for, say, chemo nausea?

Generally, no.

Not for severe cases.

And what about herbal options?

Ginger comes up a lot.

Ginger's very popular.

Commonly used for motion sickness, morning sickness, general nausea.

Any interactions to be aware of?

The main theoretical concern is that it might increase the risk of bleeding, especially someone who's already taking anticoagulant medications like Warfarin.

So something to ask about during medication reconciliation if they're on Warfarin and also using ginger supplements?

Caution.

Exactly, it needs awareness.

Okay, this is a lot of information on the drugs themselves.

How do we translate this into practical nursing actions?

Let's walk through the nursing process.

Sounds good.

Let's start with assessment.

What do you need to check before giving these drugs?

First off, baseline status is key, right?

Vital signs, definitely.

Assess their hydration, look at intake up, put skin turgor, mucous membranes.

Are they already dehydrated?

Crucial.

And connecting back to those dopamine blockers, the anti -dopaminergics and prokinetics.

Ah, the EPS risk.

Right.

You need a baseline neurological check.

Look for any existing abnormal movements before you give a drug that could potentially cause or worsen them.

Document that baseline.

Also, medication history is vital.

Check for interactions.

Many antimedics cause drowsiness.

So you need to know if they're already taking other CNS depressants or alcohol.

That combination can really increase sedation.

Good point.

And checking for those specific contraindications we mentioned?

Yes, like narrow angle glaucoma before giving scopolamine or meclosine.

That's a hard stop.

Okay, assessment done.

Now, implementation and patient teaching.

What are the key messages?

Safety first, always.

Drowsiness and dizziness are common side effects for many of these.

So, instruct patients.

No driving, no operating heavy machinery.

Be careful when getting up.

Absolutely.

And reinforce avoiding alcohol and other CNS depressants.

What about route -specific teaching, like that scopolamine patch?

Yes.

Remind them.

Clean and dry the spot behind the ear first.

Apply the patch.

And wash hands thoroughly right after applying it.

Why wash hands so carefully?

To avoid accidentally touching your eye with any drug residue.

Remember, it's an anticholinergic collie.

It can dilate pupils and blur vision if it gets in the eye.

Ah, good point.

And timing again, especially for CINV.

Can't stress it enough.

Ondansetron, a preposent, others for chemo need to be given before the treatment, usually 30 to 60 minutes prior.

Prophylaxis is key.

What about managing common side effects like dry mouth?

Very common, especially with the anticholinergics and antihistamines.

Simple measures help.

Suggest sugarless gum or hard candy, frequent sips of water.

Okay.

And finally, evaluation.

How do we know the treatment is working?

Well, the most obvious therapeutic effect is that the nausea and vomiting decrease or stop altogether.

Right.

And preventing those complications we talked about at the start, maintaining fluid and electrolyte balance.

Exactly.

But you also evaluate by monitoring for adverse effects.

Are they getting too sedated?

Are they experiencing orthostatic hypotension, especially maybe with dronabinol?

Are there any signs of EPS?

Continuous monitoring and reassessment.

Always.

Okay.

That was a really thorough walkthrough.

Let's try to boil down the main takeaways.

Sounds good.

So, core idea.

Vomiting is a reflex, but it's complex, involving multiple pathways in neurotransmitters.

ACG, dopamine D2, histamine H1, serotonin 5 -HT3, substance P, and K1.

And the anti -emetic drugs work by targeting and blocking these specific pathways.

Often, using drugs from different classes together gives better results by hitting multiple targets.

Right.

And patient safety is paramount.

We have to be incredibly vigilant about administration, especially with high alert drugs like avipromethazine.

That dilution and slow administration through a large vein, farthest port critical.

And always assessing for pre -existing conditions like glaucoma or baseline neurological status before giving certain drugs.

Okay.

So, we've covered the mechanisms, the drugs, the safety.

Before we wrap up, you usually leave us with something to think about.

I do.

So, we mentioned that some drugs, like dronabinol, or even sometimes adding benzodiazepine like lorazepam, can kind of blunt the memory of the vomiting experience.

Right.

They have some amnestic effect.

Exactly.

And we also know that anxiety and anticipatory nausea are huge factors, especially in things like CINV.

Definitely.

The fear of being sick can make you sick.

So, here's the thought.

How much of the success we see with modern anti -emetic therapy, particularly in challenging situations like chemotherapy,

actually relies on managing the

psychological response, their perception, their anxiety, their memory of the event, versus purely blocking the physical reflex arc.

Hmm.

That's interesting.

How much is physiology and how much is psychology and how intertwined are they in making someone feel better or worse?

It's something to mull over.

It highlights the holistic nature of care, doesn't it?

It really does.

A great point to end on.

Thank you for joining us for this deep dive into anti -emedics.

Go be well -informed.