Chapter 39: Drugs for Disorders of the Respiratory System

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You breathe about 20 ,000 times a day, just completely on autopilot.

Yeah, you really don't think about it.

Right.

You don't think about the mechanics of it or like the chemistry of it at all, well, until the exact moment you can't.

Which is a terrifying moment.

Oh, absolutely.

Yeah.

So today we are hacking the respiratory system.

We're looking at, you know, the chemical crowbars, the microscopic fire extinguishers, and honestly, the sheer physics of how we force oxygen back into a suffocating body.

It's a fascinating topic.

It really is.

Welcome to this deep dive.

If you are a college student tackling pharmacology for the first time, this is for you.

We're pulling our foundational knowledge today from the Lippincott Illustrated Reviews on Pharmacology.

Specifically Chapter 39, which covers drugs for respiratory disorders.

Right.

But our mission isn't just to like help you memorize a dry list of drug names.

We are building a logical ladder here.

Because pharmacology isn't just flashcards, you know, the goal is to connect the dots.

We really want to understand how the foundational respiratory physiology explains the actual drug targets.

And from there, we can see how those targets dictate the mechanisms of action.

And then how those mechanisms translate into therapeutic effects and clinical warnings.

Right.

Because if you understand the why behind the drug,

the what becomes so much easier to remember for your exams.

That makes total sense.

So to understand respiratory drugs, we have to look at the two main ways our lungs fail us.

We have acute reversible blockades like asthma and then chronic permanent damage like COPD.

And once we understand that pathology, we'll break down the crucial physical mechanics of inhalers.

Because, I mean, drug delivery is just as important as the drug chemistry itself.

Oh, entirely.

Yeah.

And finally, we'll finish up by moving up the respiratory tract to upper airway issues.

So dealing with things like allergic rhinitis and the neurological cough reflex.

Okay, let's unpack this.

We're starting with asthma, right?

Let's start there.

It is the most common chronic respiratory disease.

It affects over 235 million people worldwide.

Yeah, so it makes it the perfect place to establish our baseline for airway mechanics.

If you picture figure 39 .2 from the text,

a cross section of a completely normal airway looks like a wide open tunnel.

The walls are thin, air flows freely, all that.

Exactly.

But an asthmatic airway looks entirely different.

Asthma is at its core, a chronic inflammatory disease characterized by hyper responsive airways.

Meaning the airways like they overreact to things that normally wouldn't be a threat.

Right.

Like cold air or just a little bit of pollen.

So when an attack is actually triggered, what happens to block that open tunnel?

Well, three distinct things happen.

First, the bands of bronchial smooth muscle that wrap around the airway, they physically contract and squeeze.

Ouch.

Okay.

Second, the mucosal walls of the airway become deeply inflamed and thickened.

And third, the body just starts overproducing mucus, which fills up whatever tiny space is left.

I always think of it like trying to drink a really thick milkshake through a tiny squeezing cocktail straw.

That's a good visual.

The inside of the straw is actively swelling shut while you're trying to use it.

That is an uncomfortably accurate analogy, yeah.

So the overarching objective of our pharmacology here is reversing and preventing that inflammation.

Which is figure 39 .3, the step up approach, right?

Right.

A patient might start with intermittent asthma and as it progresses to mild, moderate or severe persistent asthma, we step up the intensity and combination of the drugs.

But okay, if a patient is actively suffocating because that smooth muscle is clamping down around the airway, they don't have time for a slow acting preventative.

No, not at all.

They need a chemical crowbar to pry the airway open right then.

And that brings us to our first drug class, the beta -2 adrenergic agonists.

Okay, the quick fix.

Exactly.

When that smooth muscle clamps down, we target the beta -2 adrenergic receptors in the lungs.

You can kind of think of these receptors as the biological relax buttons for smooth muscle.

So activating them causes direct bronchodilation.

Right.

For quick relief, we use short acting beta -2 agonists or SABAs.

Albuterol and level buterol are your classic examples here.

And those work fast, right?

Incredibly fast.

Onset is usually between 5 and 30 minutes and they provide relief for about 4 to 6 hours.

Which makes them the perfect rescue inhaler for acute bronchoconstriction.

Now delivering them through an inhaler is a very deliberate choice, isn't it?

Because if you just gave someone a pill that activated beta receptors all over their body, you'd trigger a massive systemic response.

You'd see a host of unwanted effects.

Systemic activation of beta receptors can cause tachycardia, which is a racing heart, as well as hyperglycemia and skeletal muscle tremors.

Yikes.

So you want to avoid the pills if you can.

Right.

By inhaling the drug, local delivery targets the lungs directly and largely spares the rest of the body from those systemic side effects.

That's smart.

Now alongside the short -acting rescue drugs, we also have long -acting beta -2 agonists or blabies.

These are drugs like salmeterol and formoterol, right?

Exactly.

They're basically chemical cousins to albuterol.

But their structure allows them to stay bound to the receptors and provide bronchodilation for at least 12 hours.

Wait, so if LabIs keep the airway open for 12 hours, why don't we just give everyone LabIs and skip the short -acting ones entirely?

It seems easier, right?

Yeah.

I mean, it seems way more convenient to just take it twice a day and be done with it.

Well that logic makes total sense on the surface, but it is exactly what gets people into life -threatening trouble.

Oh, really?

Why?

You have to remember that LabIs have absolutely no anti -inflammatory effects.

Zero.

They only relax the smooth muscle.

Ah, okay.

And asthma is fundamentally a disease of inflammation.

Exactly.

So if you just use a LabA, you're chemically propping the airway open while the underlying tissue is still burning with inflammation.

That sounds dangerous.

It is.

The inflammation silently worsens because the patient feels fine.

I mean, their airway is artificially held open.

Right.

But eventually the inflammation becomes so severe that no amount of bronchodilator can overcome it, and that leads to a fatal asthma attack.

Wow.

So it masks the real problem.

Completely.

Because of this, using a LabA as monotherapy, meaning all by itself,

is strictly contraindicated in asthma.

That is a massive clinical warning.

Huge.

Well, LabIs must always, always be paired with an asthma -controller medication,

specifically

an inhaled corticosteroid.

Okay, so let's talk about how we actually put out that underlying fire.

If beta -2 agonists are just, you know, propping the door open, the inhaled corticosteroids or ICS are what actually heal the tissue.

Exactly.

Drugs like sleuticosone, piclomethazone, and butynide.

They are the absolute foundation of long -term control for persistent asthma.

So how do they work?

Well, to understand figure 39 .4, imagine a factory assembly line for inflammation.

High up at the very start of this assembly line is an enzyme called phospholipates A2.

Okay.

Inhaled corticosteroids block this enzyme.

By shutting down phospholipates A2, you stop the release of arachidonic acid entirely.

So you're basically shutting off the power to the entire inflammation factory before any of the inflammatory chemicals can even be built.

That's a great way to put it.

Because of that high -level blockade, the downstream effects are massive.

You reverse mucosal edema, decrease the permeability of the capillary.

So they stop leaking fluid into the airway.

Right.

And you stop the production of inflammatory mediators called leukotrienes.

Over several months of regular use, this actually reduces the overall hyperresponsiveness of the airway smooth muzzle.

That's incredible.

But because we are systematically suppressing the immune response in the airways, there's a catch, right?

There's always a catch.

When you inhale a steroid, some of the powder inevitably deposits in your mouth and the back of your throat.

And if it just sits there, it suppresses your local immune system.

Right.

Which allows normal mouth fungus to grow out of control, leading to a condition called oropharyngeal candidaeusis.

Better known as thrush.

Yeah.

Thrush.

It also causes hoarseness.

So here's an actionable tip for your exam.

Always remember the golden rule of ICS therapy.

The swish and spit.

Yes.

Patients must rinse their mouth with water and spit it out after every single use.

It's a simple behavioral step, but it is critical for patient adherence.

Now let's go back to that inflammation assembly line.

If some arachidonic acid manages to escape that steroid blockade, the body's 5 -lipoxygenase pathway gets a hold of it and turns it into leukotrienes.

And we said earlier, leukotrienes are nasty in asthma.

Very nasty.

They violently constrict the bronchioles and cause severe swelling.

So we have alternative therapies that target this specific downstream pathway.

The leukotrine modifiers.

It's really cool how specific these are.

We have a drug called zilutone, which acts directly on the 5 -lipoxygenase enzyme itself, right?

Correct.

Preventing the leukotrienes from even being formed.

And then we have the drugs that end in leukochons, like zafralucast and montelucas.

Right.

They work a little differently.

They let the leukotrienes form, but block them from binding to their target receptors.

The cysteineleukotrine -1 receptors.

Okay.

Got it.

Any clinical warnings for these?

Yes.

An important one for your exams.

These modifiers require periodic monitoring of hepatic enzymes.

They can be pretty tough on the liver.

Oh, good to know.

If serum liver enzymes exceed three to five times the upper limit of normal, the drugs must be discontinued immediately.

Furthermore, zafralucast and zilutone both inhibit the cytochrome P450 isoenzymes.

Okay.

Let's translate that for a second.

Think of the CYP450 system as the body's chemical waste disposal unit located in the liver.

It breaks down foreign chemicals and drugs so you can clear them out.

Exactly.

If a drug like zafralucas clogs up that disposal unit, any other drugs the patient is taking will pile up in the bloodstream, leading to massive, potentially toxic drug interactions.

That is a crucial concept for pharmacology exams.

They love testing on CYP interactions.

Definitely.

Now, the text also mentions a few other alternative targets down the cascade.

Right.

Like cromalin.

It's a purely prophylactic agent.

It basically stabilizes the membranes of mast cells, stopping them from degranulating and pumping histamine into the airway.

And then there's an older bronchodilator called theophylline, which is a prime example of a drug you really have to respect.

Oh, absolutely.

We don't use it much anymore because it has a very narrow therapeutic window.

Meaning, the dose required to help the patient breathe is dangerously close to the dose that causes toxic side effects.

Yeah.

Things like severe seizures or potentially fatal cardiac arrhythmias.

Not something you want to mess with.

No.

It is also heavily metabolized by the liver, subject to numerous of those CYP drug interactions we just discussed,

and requires strict blood draws to monitor serum concentrations.

So high maintenance.

Very.

Now, moving from the oldest drugs to the newest, we have the heavy hitters for severe asthma.

The monoclonal antibodies.

To biologics.

Omalizumab selectively binds to human immunoglobulin E, or IgE, neutralizing the antibody that triggers allergic asthma.

And then you have the lizumabs, like Mipilizumab and Rizlizumab.

Okay.

Grouping by suffix is a great study hack here.

When you see Emab, think monoclonal antibody.

That's a perfect trick.

These specific lizumabs are interleukin -5 antagonists.

IL -5 is the major signaling cytokine that activates egasomophils, a type of white blood cell that drives severe asthma inflammation.

But keep in mind, these biologics are strictly reserved for severe, poorly controlled asthma.

Because of the cost.

The high cost, the fact they're administered via injection or infusion, and they carry rare but serious risks, including anaphylactic reactions.

Okay.

So that pretty much covers the reversible landscape of asthma.

But now we need to contrast that with a disease that structurally and permanently alters the lungs.

Chronic obstructive pulmonary disease, or COPD.

The key word here is irreversible.

Right.

COPD.

Figure 39 .5 outlines this well.

COPD involves a progressive, irreversible decline of FEV1, which stands for forced extratory volume in one second.

And it's heavily linked to smoking, right?

Heavily.

Over years of smoking, the actual architecture of the lungs is destroyed, leading to continuous airflow obstruction.

But the symptoms, like chronic cough, chest tightness, breathlessness, they look almost identical to asthma on the surface.

They really do.

So since it looks like asthma, do we just copy -paste the asthma drug list?

Do we just hit them with steroids to fight the inflammation?

If we connect this to the bigger picture, no.

The underlying pathology is entirely different, so the drug paradigm shifts completely.

Okay, how so?

In asthma, we said inhaled corticosteroids are the foundation because we are treating reversible inflammation.

But in COPD, bronchodilators are the foundation.

Ah.

Specifically, we use long -acting muscarinic antagonists, or LAMAs, and long -acting beta -2 agonists, LabADs.

Let's break down muscarinic antagonists for a second.

In the parasympathetic nervous system, your rest -and -digest system, muscarinic receptors cause airway smooth muscle to constrict.

So by giving a muscarinic antagonist, like Tyotropium or Meclidinium, we block that constriction.

Exactly.

Combining a LAMA with a Laba is the first -line defense for COPD to increase airflow and decrease the frequency of exacerbations.

Okay, but what about the corticosteroids?

Wouldn't it help to just add steroids to be safe?

I mean, just in case?

Actually, no, because in COPD, the use of inhaled corticosteroids carries a specifically increased risk of pneumonia.

Wait, really?

Why pneumonia?

Think about it.

A COPD patient's lungs are structurally damaged and already struggling to clear out debris and bacteria.

If you add an amino suppressant like a local steroid on top of that damaged architecture, bacteria just have a field day.

Oh, wow.

That makes a lot of sense.

ICS is restricted only to patients with severe COPD, meaning an FEV1 of less than 60 % of their predicted volume, or those who have an asthma COPD overlap syndrome.

And chronic long -term use of oral steroids is not recommended at all in COPD.

Correct.

There is one unique pill for severe COPD, though, or Flumilas.

Yes, it's an oral PDE4 inhibitor.

Right.

It works by increasing the levels of an intracellular messenger called CAMP -P.

Essentially, high levels of CAMP -P tell the lung cells to chill out and reduce inflammation.

But we should warn that it is not a bronchodilator, and it comes with tough side effects like noticeable weight loss, nausea, and diarrhea.

Good to note.

Now, all of this complex pharmacology we just discussed, blocking enzymes, agonizing receptors, tweaking intracellular CAMP -P, it is completely useless if the drug never actually reaches the lungs.

Which brings us to the art of delivery,

inhaler technique.

It sounds basic, but the physics here are wild.

Let's look at metered dose inhalers, or MDIs, versus dry powder inhalers, DPI's.

With an MDI, the medication is ejected by a pressurized chemical propellant.

It requires a very precise choreography.

You have to exhale completely, press the canister, and then inhale slowly and deeply throughout the entire actuation.

But even with perfect technique, figure 39 .6 highlights a staggering reality check from the text.

What's that?

Between 80 % and 90 % of an inhaled MDI dose is either swallowed or impacts the back of the mouth and pharynx.

Only 10 % to 20 % actually reaches the lungs.

That is insane.

80 to 90%.

And that swallowed fraction doesn't just disappear.

It enters the gastrointestinal tract, gets absorbed into the bloodstream, undergoes first pass metabolism in the liver, and gets distributed throughout the body, causing those systemic side effects we talked about.

So the solution to this physics problem is a device called a spacer, shown in figure 39 .7.

Think of a spacer like taking a sharp turn in a race car, or, you know, an antechamber or a bouncer at a club.

It's a large -volume plastic tube that attaches to the mouthpiece of the MDI.

So when you fire the inhaler into the spacer, the heavy, fast -moving propellant particles can't make the turn.

Exactly.

They physically smash into the walls of the chamber and just stay there.

But the lightweight, slow -moving drug particles float along, easily making the turn, and traveling as a gentle mist deep into the small airways.

It drastically reduces the amount of drug deposited in the mouth and swallowed.

It's such a simple fix for such a huge problem.

Now dry powder inhalers, or DPI's, require a completely different approach because they have no chemical propellant.

The patient's own breath is the engine that drives the drug.

Which means the technique is the exact opposite of an MDI.

To use a DPI, the patient must inhale quickly and deeply to physically pull the powder out of the device.

Yeah, they have to overcome the resistance of the inhaler and suck the drug into their lungs.

Okay, let's move above the lungs now.

We are traveling up the respiratory tract from the bronchioles to the nasal passages and the neurological cough reflex.

First up, Allergic rhinitis, which is inflammation of the nasal mucous membranes.

Pathologically, it starts when mast cells coated with IgE antibodies react to an inhaled allergen like dust or pollen.

They degranulate, dumping histamine and leukotrenes into the surrounding tissue.

This leads to severe mucosal edema, itchy eyes, and a runny nose.

The classic allergy symptoms.

To combat the histamine, we use antihistamines, specifically H1 receptor antagonists.

We divide these into first -generation and second -generation drugs, and the distinction is critical.

Let's start with first -generation antihistamines, like diphenhydramine.

These are generally avoided for daily use because they easily cross the blood -brain barrier.

And that causes heavy sedation and significant anticholinergic effects.

Let's translate anticholinergic for a second.

It basically means blocking the neurotransmitter acetylcholine.

Clinically, this dries everything out.

The classic memory trick for anticholinergic side effects is can't see, can't pee, can't spit, can't… Oh, you get the picture.

Aha, exactly.

Blurred vision, urinary retention, dry mouth, and constipation.

Which is why we prefer the second -generation agents.

You'll notice a lot of these share similar endings, like the edines.

Right, loratidine, fexofenadine, as well as cetirizine.

When you see those on a test, think relief without the brain fog.

They don't cross the blood -brain barrier as easily, so they avoid that sedation and impairment.

They're much better tolerated.

But if you want the absolute most effective treatment for allergic rhinitis, you bypass the pills entirely and go straight to intranasal corticosteroids.

Like fluticasone or mometazone sprays.

And here's a totally counterintuitive instruction.

When spraying these into the nose, do not inhale deeply.

Yeah, that trips people up.

You want the drug to stay in the target tissue, the nasal mucosa.

If you sniff forcefully or inhale deeply, you're just pulling the drug past the target and down into the back of your throat.

Where it gets swallowed and isn't doing anything for your rhinitis.

Exactly.

Now, for quick, temporary relief of severe nasal congestion, we have the alpha -adrenergic agonists, the decongestants like phenylephrine or oxaminazaniline.

These work by aggressively constricting the dilated, swollen blood vessels in the nasal

to physically shrink the tissue and reduce airway resistance.

But they come with a crucial clinical warning.

Intranasal decongestants must not be used for more than three days.

Why only three days?

Prolonged use causes the receptors in the nose to downregulate, leading to a condition called rhinitis medicamentosa.

Oh, rebound nasal congestion.

Exactly.

A severe rebound congestion that happens when the drug wears off, which can actually be worse than the original symptom that made you take the drug in the first place.

Talk about backfiring.

Okay, finally, let's talk about drugs for cough.

The core philosophy here is that coughing is a beneficial defense mechanism, right?

Yes.

It clears irritants, clears mucus, and expels bacterial infections.

So the priority is always to treat the underlying cause first, not just suppress the symptom.

But when a cough is dry, hacking, and keeping a patient awake, suppression is appropriate.

Right.

We have centrally acting agents and peripherally acting agents.

Centrally, meaning working in the brain, we look at opioids.

Like codeine.

It decreases the sensitivity of the cough center in the central nervous system.

And it achieves this antitusive effect at doses lower than what you need for pain relief.

But the risks remain exactly the same, right?

High addiction potential, sedation, and constipation.

Unfortunately, yes.

Then there's dextromethorphan.

It's a synthetic derivative of morphine.

But it has no analgesic or pain relieving effects.

Right.

It is equal in efficacy to codeine for suppressing a cough, but it has a significantly lower abuse potential at regular doses, though it can still cause dysphoria and be abused at extreme doses.

You'll often see both of these combined with guifinicin.

Which is an expectorant.

It helps thin out thick mucus so you can actually cough it up and get it out.

Moving away from the brain to peripheral action, we have a drug called benzonatate.

This one is interesting.

Unlike the opioids, benzonatate actually anesthetizes the physical stretch receptors located in the respiratory passages, lungs, and pleura.

It literally numbs the trigger that tells your brain to cough.

It does.

It comes in a small, liquid -filled capsule.

And there is a major danger here.

Wait, if it's an anesthetic, what happens if a patient accidentally chews the capsule?

That's the danger.

If a patient chews it or it breaks in their mouth, the liquid inside will rapidly release and completely numb the tongue, mouth, and throat.

Which means they lose their gag reflex and their ability to swallow.

Right, leading to a massive choking hazard and a compromised airway.

The capsules must always, always be swallowed whole.

Good to know.

So what does this all mean?

When we look back at the logical ladder we've built today, it becomes clear that respiratory pharmacology is an exercise in pinpoint targeting.

It really is.

Whether you are using a dry powder inhaler to hit beta -2 receptors in the bronchioles, or blocking the 5 -lipoxygenase enzyme in the cytosol to stop leukotrenes, or using benzonatate to numb peripheral stretch receptors.

The success of the drug completely depends on understanding exactly where and how it works.

Exactly.

And to wrap up, we want to leave you with one final provocative thought to mull over.

Yeah.

Given how incredibly specific the inhaler technique needs to be for these drugs to even reach their cellular targets.

Remembering that up to 90 % of an MDI dose can just end up crashing into the back of the throat and being swallowed?

Right.

How much of perceived treatment failure in the real world isn't a failure of pharmacology at all?

How much of it is actually just physics and fluid dynamics working against improper inhalation?

Wow.

That's a great point.

It's a fascinating question, and one that highlights why patient education is just as critical as prescribing the right molecule.

Because the best drug in the world won't work if it doesn't reach the target.

Exactly.

Well, on behalf of the last minute lecture team here at The Deep Dive, thank you so much for joining us.

We wish you the absolute best of luck on your pharmacology exam.

You're going to do great.

Remember, you breathe 20 ,000 times a day, and now you know exactly what is happening under the hood.

Keep breathing and keep studying.