Chapter 37: Antihistamines, Decongestants, Antitussives & Expectorants

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Welcome back to The Deep Dive.

Today, we're cracking open Lilly's Pharmacology for Canadian Health Care Practice Chapter 37 specifically.

We're going deep on meds for upper respiratory infections,

common cold, allergies,

that kind of misery.

Okay, so let's unpack this.

Our mission, really, is to give you, the listener, a clear path through the, let's say, four big groups of drugs for these symptoms.

We're talking antihistamines, decongestants, antitussives, and expectants.

Basically, understanding the why behind picking one cold medicine over another.

Exactly, and, you know, it's crucial to remember what we're actually dealing with.

URIs, they're mostly viral.

Rhinovirus, influenza, things like that.

So these drugs, they don't cure the virus itself.

It's what we call empirical therapy.

We see the symptoms, the inflammation, too much mucus, the stuffiness, the cough, and we treat those.

We're managing the fallout, not attacking a root cause, the virus.

And before we even touch the drug classes, there's a huge public health point from Health Canada we absolutely have to mention.

It's really critical.

They strongly advise against giving over -the -counter cough and cold stuff to kids under six.

The risks are serious,

like over -sedation, seizures, even heart rhythm problems.

That's the essential safety baseline.

Okay, so with that covered, let's start with antihistamines, H1 blockers specifically.

If you're dealing with allergic rhinitis, hay fever, this is probably your go -to category.

So histamine itself, what's its deal?

Well, histamine is a big player.

It's involved in nerve signals,

making capillaries leaky, contracting smooth muscles, stimulating secretions, lots of things.

But for allergies, we focus on the H1 receptors.

That's right.

H1 receptors are the ones mainly involved in smooth muscle contraction, think lungs or stomach, and that capillary dilation that causes the classic allergy symptoms, the swelling, the redness.

H2 receptors are more about heart rate and stomach acid.

And when way too much histamine gets released, like an anaphylaxis, what happens then?

Oh, that's serious.

You get widespread,

smooth muscle constriction, like in the lungs, making it hard to breathe,

massive increase in secretions, vasodilation everywhere, causing blood pressure to plummet, and fluid leaking out, causing edema, swelling.

Okay, so how do the H1 antagonists, the antihistamines we take,

actually work against this?

It's interesting.

They don't actually reverse what histamine does once it's locked onto a receptor.

Instead, they're like competitive blockers.

They race against histamine to grab onto those unoccupied H1 receptor sites on cells like mast cells and basophils.

Ah, so they prevent histamine from binding in the first place.

Exactly.

Which tells you something really important about using them.

Timing.

Timing.

They work best if you take them early, ideally before that whole histamine cascade really gets going and fills up all the receptor spots.

They're preventative in that sense.

No, they're different types, right?

The ones that knock you out and the newer ones.

Correct.

We usually split them into two main groups based on, well, largely on whether they make you sleepy.

Let's start with the older ones, the traditional antihistamines, like a defenhydramine, Benadryl.

Right, that's a classic example.

These work peripherally, hitting those allergy symptoms, but they also easily cross the blood brain barrier.

And that central action is why they cause drowsiness, sedation.

People actually use that effect sometimes, don't they, for sleep?

They do.

And that central anticholinergic effect is also why they're used for things like motion sickness, sometimes even for Parkinson's symptoms.

But.

There's always a but.

There's a big but, especially for older adults.

Right.

That sedation, plus what we call a hangover effect,

significantly bumps up the risk for dizziness, confusion, and falls.

So they're generally not recommended for the elderly.

Okay, then you've got the non -sedating ones.

Loratadine comes to mind.

Claritin.

Yes, Loratadine, setyrazine, fexofenadine.

These were a huge step forward.

The key difference is that they were designed not to easily cross the blood brain barrier.

How does that work?

They're often larger molecules or they get actively pumped out of the brain.

So they still block H1 receptors out in the body for allergy relief, but they cause much less action in the central nervous system, less sedation.

That sounds like a win -win.

It generally is.

Plus, many of them last longer, often allowing for just once a day dosing.

That's great for adherence, making sure people actually take their meds consistently.

But even with the non -sedating ones, there are still those anti -cholinergic side effects, right?

The drying effects.

Oh, absolutely.

You still get those because you're blocking cholinergic receptors peripherally.

Think dry mouth, maybe changes in vision, difficulty urinating, which is a big watch out for men with prostate issues and constipation.

The can't see, can't pee, can't spit, can't, you know.

Got it.

Okay, so antihistamines handle the allergic reaction, dry things up.

But what about pure congestion when your nose is just blocked solid because everything's swollen?

Right, blocking histamine won't shrink swollen tissues.

For that, you need decongestants.

And there are broadly three kinds we look at.

Idrenergics, which are very common, anticholinergics, less so for congestion alone, and intranasal steroids.

Let's focus on the main ones, the adrenergics, like oxymethazoline in nasal sprays.

Exactly.

Oxymethazoline, pseudoephedrine, which used to be everywhere.

These are sympathomimetics.

They mimic the sympathetic nervous system.

Specifically, they stimulate alpha adrenergic receptors.

And what does stimulating alpha receptors do in the nose?

It causes vasoconstriction.

It makes the little arterioles, the tiny blood vessels supplying the nasal sinuses, clamp down.

Less blood flow means the swollen and gorge nasal membranes shrink, and that opens things up so mucus can drain.

Okay, but how you take them matters a lot here, doesn't it?

Oral versus spray.

Hugely important difference.

If you take an oral decongestant, like pseudoephedrine tablets, the effect takes longer to start, maybe isn't quite as potent, but it lasts longer.

And the big plus,

virtually no rebound congestion.

Rebound congestion, the spray problem.

The spray problem.

Topical sprays, like that oxymethazoline, work fast and are potent.

But because they're absorbed quickly, right there in the nose, the effect can also wear off relatively fast.

This can lead people to use the spray more and more often.

Because they feel congested again as it wears off.

Precisely.

And then you get into this cycle where the drug itself starts causing the congestion to worsen when it wears off.

It's called rhinitis medicamentosa.

Real dependency can develop.

It's nasty.

So sprays are quick relief, but short -term use only.

What about the intranasal steroids like fluticasone, Flonase?

Now these are different.

They don't cause that immediate vasoconstriction.

Instead, they target the underlying inflammation.

They work over days to make the immune cells in the nasal lining less responsive, reducing swelling and symptoms more gradually, but more sustainably.

And no rebound risk.

No rebound risk associated with them, which is a major advantage for chronic issues like persistent allergies.

They're often a first -line treatment for that.

Okay.

Back to the adrenergic for a sec.

A key nursing point you mentioned.

Yes.

Because they stimulate alpha adrenergic receptors, even the nasal sprays, if overused and definitely the oral forms, can have systemic effects.

You're hitting alpha receptors elsewhere in the body.

Meaning?

Meaning you can get side effects like nervousness, trouble sleeping, palpitations, and importantly,

increased blood pressure.

So definitely not for everyone.

Absolutely not.

Oral adrenergic decongestants are a big no -no for people with uncontrolled high blood pressure, certain heart conditions, or things like acute angle glaucoma.

That vasoconstriction is dangerous for them.

Okay.

Let's switch gears to coughing.

Sometimes a cough is good, right?

Clear stuff out.

A productive cough, yes, it serves a purpose, but sometimes a cough is just dry, irritating, non -productive.

Or maybe it's harmful, like after abdominal surgery where coughing could strain stitches.

In those cases, we might want to suppress it with antitussives.

And again, different types here, opioids and non -opioids.

That's the main split.

First, you have opioid antitussives.

Codeine is the classic example, sometimes hydrocodone.

They work directly on the cough center in the brainstem, the medulla, to suppress the cough reflex.

And they have other effects too.

Yes.

They also provide some pain relief, analgesia, and they tend to have a drying effect on the mucous membranes, which can sometimes help with a runny nose, but can also thicken secretions.

There's a big warning about codeine in kids, though.

A very significant one.

Codeine itself isn't the main active part.

The body has to metabolize it into morphine using an enzyme CYP2D6.

But people vary wildly in how active that enzyme is.

Some are ultra -rapid metabolizers and get a huge morphine hit from a standard dose.

Extremely dangerous, especially in children.

It can lead to profound respiratory depression, sedation, even death.

That's why Health Canada strongly advises against using codeine in any 1 under 12.

Wow.

What about the non -opioid antitussives,

like dextromethorphin, DM, and cough syrup?

Right.

Dextromethorphin or DMX.

It also acts on the cough center in the brain, similar location to opioids, but through a different mechanism.

Crucially, at normal therapeutic doses, it doesn't have the pain relief or the significant CNS -depressant effects of opioids.

So generally safer for suppressing a cough?

At recommended doses, yes.

It's considered safe and non -addicting for its intended purpose.

However.

Oh, it's another however.

Yeah.

Dextromethorphin has unfortunately become a significant drug of misuse, especially among young people.

Robo -tripping, skittling, taking massive doses way beyond what's recommended.

What does it do at high doses?

It acts as a dissociative anesthetic, kind of like PCP or ketamine.

People experience altered perceptions, poor coordination, confusion, and at very high doses, hallucinations, seizures, coma.

It's a serious public health issue.

So even over the counter doesn't always mean risk -free.

Important nursing point with antitussives.

Definitely.

With the opioid ones, remember they potentate.

They increase the effects of other CNS -depressants, alcohol, sleeping pills, sedatives.

You have to assess carefully.

If someone already has breathing problems like COPD or is prone to low oxygen levels, adding an opioid antitussive could be really risky.

Okay, so we've blocked allergies, shrunk swelling, suppressed dry coughs.

What if the cough is productive, full of gunk, and you want to help get it out?

That's where expectorants come in.

Their whole job is to help you expectorate, to cough up phlegm more effectively.

And the main player here is guifinesin, mucinex, roboticin, chest congestion.

That's the one, guifinesin.

Its main action is thought to be increasing the flow of respiratory tract fluid and reducing the viscosity, the thickness of the secretions, makes them thinner and easier to move.

How does it do that?

The mechanism described in lilies often involves reflex stimulation.

The idea is that guifinesin irritates the stomach lining slightly.

Irritates the stomach to help the lungs.

Kind of counterintuitive, right?

But that GI irritation is thought to trigger a reflex via the vagus nerve that leads to increased secretions in the respiratory tract, thinning out the mucus.

Interesting.

So its main use is for those wet, productive coughs from colds like bronchitis.

Exactly.

To make the cough more productive, easier to clear things out.

One thing to note is its half -life is pretty short, only about an hour.

Which means you have to take it fairly often.

Yes.

That's why dosing is usually every four to keep levels up.

Side effects are generally minimal, maybe some nausea or stomach upset linked to that GI irritation mechanism.

Okay, so we've covered the four big categories.

How do we tie this all together from a nursing perspective?

What's the synthesis?

It really comes back to the nursing process.

Assessment is paramount.

Before recommending or giving any of these, you've got to rule out something more serious.

Is this just a cold or could it be pneumonia?

Is that wheezing?

Actually an asthma attack needing a bronchodilator, not just a decongestant.

Good point.

And specific takeaways for assessment based on the drugs.

You mentioned older adults and traditional antihistamines.

Right.

With traditional antihistamines, watch older adults like a hawk for confusion, dizziness, paradoxical excitement even.

And remember that drying effect in someone with COPD or pneumonia, overly thick secretions can actually block airways, increasing infection risk.

And for decongestants.

Blood pressure, heart rate, always assess.

Even with topical sprays, check if they have controlled hypertension.

Oral forms are generally a bad idea for anyone whose blood pressure isn't well managed.

A patient with controlled hypertension might maybe use a spray short term with prescriber okay, but oral is usually discouraged.

So assessment is key.

What about patient teaching, implementation, evaluation?

Huge.

First, fluids, fluids, fluids.

Unless they have a fluid restriction for some reason, encourage drinking lots of water, maybe up to 3000 mL a day.

Hydration is honestly one of the best expectorance there is.

It helps thin secretions naturally.

Simple but effective.

What else?

The rebound congestion risk with sprays needs explicit counseling.

Tell them.

Use this exactly as directed for no longer than three, maybe five days max.

Make sure they understand why.

And when should they call the doctor or nurse practitioner?

If symptoms get worse, if they develop a high fever, say over 38 Celsius or 100 .4 Fahrenheit, or if the symptoms just drag on for more than say three or four days without improvement,

could be something bacterial setting in.

And the combination products,

those can be tricky.

Very tricky.

The shelves are full of pills and syrups with two, three, even four of these drug classes mixed together.

Patients must be taught to read the active ingredients.

You don't want them taking a combo pill with acetaminophen and then also taking acetaminophen for a headache, right?

Or taking a nighttime cold med with an antihistamine and then having a glass of wine.

Doubling up on sedation or other effects.

Exactly.

Avoid dangerous combinations, check labels, understand what's in there, and avoid mixing with alcohol or other sedating drugs unless cleared by a professional.

Okay, so quick recap.

We've got H1 blockers, sedating and non -sedating for allergies.

Audrenergic decongestants for stuffiness, watching out for rebound and BP,

antitussives, opioid and non -opioid for stopping dry coughs, with cautions for codeine and DMX, and expectorants like Wifanesin to help clear out productive coughs.

That covers the main tools in the Symptomatic Toolbox from this chapter.

So here's the final thought for you, our listener, to chew on.

Given that almost all these cold treatments are just empirical therapy managing symptoms, not curing the virus, what critical thinking skills are most vital when you or your patients are standing in that pharmacy aisle faced with dozens of different OTC combination products?

How do you choose wisely?

It really comes down to understanding the why behind each ingredient.

Knowing what symptom each drug targets helps you pick what you actually need and avoid what you don't.

Thanks for joining this last minute lecture team deep dive.

Yeah, thank you for tuning in.

We'll catch you on the next deep dive.