Chapter 54: Drugs for Angina Pectoris

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You know, usually when we think about a mechanical pump, we picture this constant forward motion.

It pushes fluid out, it pulls fluid in, and it's just constantly feeding itself to keep the motor running.

It's continuous.

Right.

Yeah.

It's a closed, relentless loop.

As long as the engine is running, the fuel is flowing.

But then you look at the human heart and suddenly that simple mechanical logic just gets flipped upside down.

The heart is a pump, sure, but the way it feeds itself with oxygen is honestly a little counterintuitive.

It really is.

It is the absolute definition of a biological paradox, and that paradox is exactly why treating heart pain, what we call angina, is so incredibly complicated.

Welcome to the Deep Dive.

Today we're doing a special installment for all the nursing students out there, so consider this part of our Last Minute Lecture series.

Whether you're listening on your way to clinicals or furiously prepping for a pharmacology exam, you are in the exact right place.

Our mission today is crystal clear.

We are going to master the pharmacology of drugs used for angina pictoris.

Yeah.

And we're focusing exclusively on the foundational concepts you'd find in Chapter 54 of Lane's Pharmacology for Nursing Care.

Exactly.

Because we know this material can feel, well, really dense.

It's usually packed with biochemical pathways, adverse effects, and life -or -death drug interactions.

Oh, absolutely.

It's a lot to take in all at once.

So we are going to translate all of that text -heavy pharmacology into plain conversational language.

No outside distractions, just the exact concepts you need to understand so the reasoning behind Safe medication decisions becomes like second nature.

But you know, before we can even think about memorizing drug names and dosages, we have to understand the fundamental physics of the heart.

You really can't fix a machine if you don't know how it's broken.

Okay, let's unpack this.

The core concept of angina always comes down to a really delicate balancing act.

Cardiac oxygen supply versus cardiac oxygen demand.

That's the entire game right there.

Anginal pain happens when the oxygen supply to the heart is just, well, insufficient to meet the oxygen demand, the muscle starts starving, basically.

And that starvation translates to severe chest pain.

So what determines that balance?

Because oxygen demand is driven by four major factors, right?

Heart rate, contractility, preload, and afterload.

Exactly.

But oxygen supply is determined by just one thing, which is myocardial blood flow.

And here is the part that kind of blows my mind.

The actual perfusion -like, the feeding of the heart muscle with oxygenated blood only takes place during diastole when the heart is relaxed.

Is it like trying to fill a water balloon while you're squeezing it tightly in your fist?

The water can only go in when you relax your grip.

That is a perfect analogy.

Honestly, during systole, when the heart muscle violently contracts to push blood out to the rest of the body, those tiny coronary vessels that supply the myocardium are physically squeezed shut by the muscle itself.

Yeah, blood cannot flow through a pinched hose.

So the heart only gets its oxygen when it rests.

This makes treating angina super tricky because if the heart beats too fast, you lose that vital resting time.

Right, because the squeeze happens too often.

Exactly.

And the relax and feed phase gets cut dangerously short.

So imagine a seesaw.

On one side is oxygen supply, on the other is demand.

In a healthy heart, if you go for a sprint, your oxygen demand goes way up.

To balance the seesaw, your coronary arterioles dilate, increasing blood flow and oxygen supply by like four to five times.

The seesaw stays level.

But in a heart with coronary artery disease or CAD, it's a completely different story.

With CAD, a plaque is already partially blocking the arteries.

So to compensate,

just while you were sitting on the couch doing nothing, those arterioles downstream from the plaque are already fully dilated.

Just to keep up with resting demand.

Just to meet resting demand.

They are totally maxed out.

So when that person goes for a sprint, there's no more dilation left.

Oxygen demand skyrockets, but supply cannot increase to match it.

The seesaw tips, the muscle starves, and you get ischemic pain.

And that specific scenario is the first of the three phases of angina, which is chronic stable angina, also called exertional angina.

Because the arteries can't dilate any further, our treatment goal here isn't to increase supply.

Right.

We physiologically can't.

So the goal is to decrease oxygen demand.

Exactly.

We have to lighten the workload.

Then you have the second type, which is variant angina, also known as Prince metals or vasospastic angina.

This one isn't caused by a fixed plaque, actually.

Really?

No, it's caused by coronary artery spasms.

It can happen at any time, even while you are like fast asleep.

So the seesaw tips the other way.

The treatment goal for variant angina isn't to decrease demand, then it's to increase oxygen supply by relaxing that spasm.

Spot on.

And just to briefly touch on the third type, unstable angina.

This is a medical emergency involving severe CAD, unpredictable spasms, and active blood clots.

Sounds terrifying.

It is.

The risk of death is much higher there.

But for our focus today, we are really zeroing in on the pharmacology for stable and variant angina.

Since stable angina is a demand problem and variant angina is a supply problem, we clearly need tools to manipulate both sides of this seesaw.

And that leads us straight into the oldest, probably most famous anti -anginal drug out there, nitroglycerin.

The absolute classic.

I mean, it's been used since 1879 and is still the drug of choice for acute attacks.

But how it actually works is a massive point of confusion for a lot of students.

It really is.

I always assumed that if someone was having chest pain from a blocked coronary artery, giving them nitroglycerin would just, you know, dilate that blocked artery and let the blood through.

Most people think that.

But the pharmacology actually says that in stable angina, nitroglycerin doesn't dilate the blocked coronary arteries at all.

In fact, if you inject it directly into the coronary artery during an attack, it doesn't relieve the pain.

So how on earth is it working?

Well, here's where it gets really interesting.

Nitroglycerin works on vascular smooth muscle, but primarily on the veins, not the arteries.

Wait, the veins?

Yes.

When nitroglycerin enters the vascular smooth muscle, it undergoes a chemical reaction.

It requires a specific cellular helper,

so hydro groups,

to be converted into its active form, which is nitric oxide.

Oh, no trick oxide, the ultimate biological vasodilator.

Exactly.

That nitric oxide activates an enzyme that elevates a messenger molecule called CGMP.

Elevated CGMP then leads to the dephosphorylation of light chain myosin.

Okay, that is getting into some heavy cellular biology right there.

Let me see if I can translate that for a second.

If CGMP is like a stand down order for the muscle fiber,

then dephosphorylating the myosin is essentially like unhooking the molecular velcro that keeps the vein pulled tight.

That's a great way to visualize it, yeah.

The molecular velcro unhooks and the vein just relaxes and widens.

But wait, how does dilating the veins in, say, my legs help the starving heart in my chest?

Because it pools the blood in the periphery.

Think about it, if your veins are dilated and relaxed, gravity keeps more of that blood down in your limbs, less blood is returning to the heart.

Oh, I see.

Yeah, that decreases the ventricular filling, which means there is less physical stretch on the heart muscle right before it pumps.

And we call that stretch preload.

Exactly.

Preload.

By dropping the preload, the heart doesn't have to work as hard to push the blood out, the workload drops, and you've dramatically decreased cardiac oxygen demand.

That makes a lot of sense.

It fixes the demand problem in stable angina by just lightening the load.

But for variant angina, the vasospasms, does it work the same way?

Actually, no.

In variant angina, nitroglycerin does directly relax the coronary spasms, thereby increasing oxygen supply.

So it is highly versatile.

That's amazing.

But as a nurse, understanding the pharmacokinetics is where it gets real.

Let's talk about the liver.

Nitroglycerin is highly lipid soluble, meaning it crosses cell membranes incredibly easily but it has a massive first pass effect.

Huge first pass effect.

If a patient swallows a standard nitroglycerin pill,

organic nitrate reductases in the liver will destroy almost all of it before it ever reaches the systemic circulation.

It just gets shredded.

Totally shredded.

That's why the plasma half -life is only like five to seven minutes.

So if the liver destroys the drug, how do we actually get it into the bloodstream to stop an acute attack?

We have to bypass the liver entirely, right?

Precisely.

That's why rapid onset formulations, the ones used to abort an ongoing attack, are given as sublingual tablets, sublingual powder, or a translingual spray.

Under the tongue.

Right.

Because they are absorbed directly through the oral mucosa under the tongue, they skip the stomach and the liver entirely and go straight into the bloodstream.

Which explains why a sublingual dose can be tiny, just like 0 .3 milligrams, whereas if you are using a sustained -release oral capsule for long -term prevention, the dose has to be massive just to survive the liver shredder.

And beyond pills and sprays, we use transdermal patches and topical ointments for sustained long -acting prophylaxis to prevent attacks before they even happen.

Oh, and you might also see drugs called isosorbide mononitrate or isorbide dinitrate in the text.

Are those basically the same thing?

Pharmacologically, yes.

They have the exact same actions as nitroglycerin, just different time courses for how long they stay in the body.

Okay, let's talk about adverse effects, because if you're powerfully dilating veins all over the body, there have to be consequences.

Oh, there definitely are.

There are three main ones.

First is intense headache.

Dilating the veins in the head causes this initially, though it usually diminishes over a few weeks.

Can they take anything for it?

Yeah, you can treat it with a mild analgesic like acetaminophen.

Second is orthostatic hypotension.

Because blood is pooling in the veins, when the patient stands up suddenly, their blood pressure drops.

Which causes dizziness or fainting?

Right.

And the third one is actually a physiological reaction to that blood pressure drop, right?

Reflex tachycardia.

The body just panics.

Exactly.

The baroreceptors in the blood vessels sense the sudden drop in blood pressure and tell the sympathetic nervous system to speed up the heart to compensate.

But remember our earlier physics lesson.

Speeding up the heart increases oxygen demand.

Yes.

Which completely negates the benefit of the drug we just gave.

So how do we stop the heart from speeding up?

Pre -treatment with a beta blocker or a calcium channel blocker can prevent that sympathetic cardiac stimulation.

Okay, we'll get to those drugs in a second, but first we need to talk about the massive safety alert regarding nitrates in the textbook.

It's a huge contraindication involving phosphodiesterase type 5 inhibitors or PDE5 inhibitors.

Drugs like sildenafil, commonly known as Viagra.

Yes, the biochemical synergy between these two drugs is fatal.

What's fascinating here is that, well, remember earlier when we said nitroglycerin works by increasing the formation of CGMP to cause the veins to relax.

Right, the stand down order.

Well, PDE5 inhibitors work by stopping the breakdown of CGMP.

So if you take them together, you are increasing the production of the stand down order while simultaneously stopping the body from clearing it away.

The CGMP levels just skyrocket and the molecular Velcro completely vanishes.

Exactly.

It leads to excessive systemic vasodilation.

The blood pressure flummets to life -threatening levels.

The concurrent use of these drugs is absolutely contraindicated.

That is definitely a test question.

Now, another big issue with nitrates is tolerance.

If nitroglycerin is so effective at preventing angina, why can't a patient just slap on a transdermal patch and wear it 247?

Because of those sulfhydryl groups we talked about earlier.

Tolerance develops rapidly, literally over a single day.

The body simply depletes its supply of sulfhydryl groups in the vascular smooth muscle.

Wow, that fast.

Yeah.

Without them, the nitroglycerin can't be converted into nitric oxide and the drug becomes entirely useless.

So the body just neutralizes it.

To prevent this, patients absolutely must have an 8 -12 hour nitrate -free interval every single day.

Yes.

That is crucial.

Usually that means taking the patch off overnight while they sleep, allowing the body time to replenish its sulfhydryl groups.

Got it.

And speaking of administration, since nitroglycerin is highly volatile, meaning it degrades quickly when exposed to light and moisture, how do you think it needs to be stored?

Well, it would have to be in a dark, tightly sealed bottle at room temperature.

Exactly.

And for the topical ointment, nurses use a specialized applicator paper with measurements on it.

Let me guess why.

Since the drug is highly lipid -soluble and crosses skin easily, if a nurse rubs the ointment onto the patient with their bare hands, the nurse is going to absorb a massive dose.

They'll dilate all their own veins and pass out from the blood pressure drop right on the clinical floor.

A very bad day at work, yes.

Always use the applicator paper.

Okay.

So nitroglycerin is incredible for immediate relief and reducing preload, but what if we want to change the baseline?

What if we want to prevent the oxygen demand from spiking in the first place by controlling the engine itself?

That moves us to the long -term protectors, beta blockers and calcium channel blockers.

Let's start with beta blockers, like Metaprolol and Procranolol.

These are first -line drugs for exertional stable angina, and they're given on a fixed schedule.

And they work by blocking beta -1 receptors in the heart.

Since beta -1 receptors are essentially the sympathetic nervous system's gas pedal, blocking them directly decreases both heart rate and contractility.

And here is a brilliant double benefit.

By slowing the heart rate, you aren't just decreasing oxygen demand.

Because the heart is beating slower, it spends significantly more time in diastole.

The resting phase.

And as we established with our water balloon analogy, diastole is the only time the heart actually gets perfused.

So beta blockers decrease demand while simultaneously increasing oxygen supply time.

Plus, they prevent that reflex tachycardia caused by nitroglycerin.

It's a total win -win, but you know, there are adverse effects.

Blocking zeta -1 receptors can cause bradycardia, a dangerously slow heart rate, and AV block.

And if you use a non -selective beta blocker that also hits beta -2 receptors in the lungs, it can cause bronchoconstriction.

So if a patient has severe asthma, a non -selective beta blocker could trigger an asthma attack.

Exactly.

You have to be very careful with asthmatic patients.

They can also mask the signs of hypoglycemia in diabetic patients, hiding the warning signs of low blood sugar.

Now, what about calcium channel blockers, or CCBs, drugs like verapamil, diltiazem, and nefetapine?

Their main action is blocking calcium channels in vascular smooth muscle.

Calcium is what allows muscles to contract forcefully.

By blocking it, the muscle relaxes.

But unlike nitroglycerin, which dilates veins, CCBs primarily dilate arterioles.

So if dilating veins decreases preload, dilating arterioles decreases afterload.

Afterload being like the physical resistance or pressure the heart has to pump against to get blood out to the body?

Precisely.

By dilating the arterioles, peripheral resistance drops, and the heart doesn't have to push as hard.

Oxygen demand goes down.

CCBs are great because they treat stable angina by decreasing demand, and they treat variant angina by relaxing the coronary spasms.

Wait, hold on.

Let me push back on something here.

Sure.

If a patient is taking a beta blocker that slows the heart, and we give them a CCB like verapamil or diltiazem, which also act directly on the heart to slow it down, aren't we risking stopping the heart entirely?

Why would a provider ever stack these?

That is a phenomenal catch, and it's a huge clinical red flag in the text.

Combining a beta blocker with a heart -slowing CCB like verapamil is highly risky because of that exact synergistic suppression of the heart rate.

If a provider needs to add a CCB to a beta blocker regimen to control pain,

they will almost always choose a dihydropyridine CCB like nifedipine.

Why nifedipine?

Because nifedipine primarily targets the blood vessels to decrease afterload and has very little direct effect on the heart rate itself.

It's a much safer combination.

Okay, that makes total sense.

But I'm noticing a trend here.

Nitrates drop your blood pressure, beta blockers drop your heart rate, CCBs drop your blood pressure and sometimes your heart rate.

Every single one of these drugs messes with hemodynamics.

Is there anything that treats angina without, you know, tanking your vitals?

That brings us to renolazine.

It's the first new class of anti -anginal approved in over a quarter century, and its mechanism is completely different.

The new kid on the block, how does it bypass the hemodynamics, Isa?

Well, it doesn't lower heart rate and it doesn't lower blood pressure.

While its exact mechanism is still being mapped out, it works by reducing the accumulation of sodium and calcium inside the myocardial cells themselves.

Oh, inside the cells.

Yeah.

Since high intracellular calcium forces the heart to burn more energy, keeping calcium levels lower helps the heart muscle generate and use energy much more efficiently.

It's working at the metabolic level, not the hemodynamic level.

That sounds like a magic bullet, but knowing pharmacology, there has to be a catch.

A significant one.

Renolazine prolongs the QT interval on an EKG, which essentially means it extends the time it takes the heart's electrical system to recharge.

Which is dangerous.

Every.

This puts the patient at risk for a serious,

potentially fatal, ventricular dysrhythmia called torsades de pointe.

And how is it metabolized?

It is extensively metabolized in the liver by a major enzyme called CYP3A4.

Oh, wait a minute, didn't we just say that calcium channel blockers are often used alongside other drugs for angina?

Don't most CCBs inhibit that exact CYP3A4 enzyme?

You've hit on another major drug interaction.

Yes, most CCBs inhibit the exact enzyme needed to clear ranolazine from the body.

Wow.

So if you combine them,

the liver can't break down the ranolazine, it builds up to toxic levels and vastly increases the risk of that fatal dysrhythmia.

So what's the work around there?

If a provider absolutely must combine ranolazine with a CCB, the only generally safe CCB to use is amlodipine, because it doesn't inhibit the CYP3A4 enzyme as aggressively.

Okay, so now we have all these individual puzzle pieces.

We've got nitrates, beta blockers, CCBs, and ranolazine.

But if we connect this to the bigger picture, how does a nurse or a provider actually put all this together for a patient in the real world?

We have to recognize the two distinct clinical goals of therapy.

The first goal is preventing myocardial infarction, a heart attack, and preventing death.

The second goal is preventing myocardial ischemia and the actual angina pain.

And preventing MI and death is actually more important than just reducing the pain.

You can live with chest pain, you can't live with a dead heart muscle.

Absolutely.

So to prevent MI, almost everyone gets an antiplatelet drug, usually aspirin or clorpidogrel, to stop clots from forming on those plaques.

They also get a cholesterol -lowering drug, like a statin, to stabilize the plaque itself.

Makes sense.

And many get an ACE inhibitor, which has been shown in major trials like the HOBAT trial, to significantly reduce the risk of stroke, MI, and cardiovascular death, especially in patients with diabetes, by reducing pathological changes in the heart muscle.

So that's the baseline survival therapy.

Now what about the pain management algorithm, the flow plan?

It's a stepwise approach.

Step one,

every patient gets sublingual nitroglycerin for breakthrough acute pain.

For baseline prevention, the preferred first choice is a beta blocker, especially if they've had a prior MI.

But what if that fails to control the pain?

Or what if they have a contraindication, like severe asthma?

Then we move to step two, which is to add or substitute a calcium channel blocker.

If that still fails, step three is to add a long -acting nitrate, like a daily transdermal patch.

And if all three of those fail to control the pain?

Then you are looking at surgical revascularization, like a CBG coronary artery bypass graft, or a PCI percutaneous coronary intervention, where they go in and place a stent.

But throughout this entire process, nurses are constantly tailoring the drugs to the patient's coexisting conditions.

You don't treat angina in a vacuum.

If a patient has asthma, you avoid beta blockers and lean on CCBs.

If they have a dangerously slow heart rate, you avoid verapamil and diltiasm, and use nifedipine instead.

Exactly.

It's about matching the mechanism of the drug to the specific physiological landscape of the patient.

Let's quickly review the major patient teaching points, because as a nurse, you are the final safe -to -check before the patient goes home.

If a patient is prescribed sublingual nitroglycerin, they need to know to place it under the tongue and let it dissolve.

Right.

And if they swallow it, it's completely destroyed by the liver.

Exactly.

They take one tablet as soon as the pain starts.

And here's the critical rule.

If the pain is not relieved in exactly five minutes, they need to call 911 immediately.

While waiting for EMS, they can take a second tablet, and five minutes later, a third.

But the maximum is three doses.

This has been an incredibly comprehensive journey.

Before we wrap up, I want to leave everyone with one final thought based on what we've covered today.

For me, the most fascinating takeaway is the reality of drug tolerance, specifically with nitroglycerin.

I mean, we are talking about a profoundly powerful chemical that forcefully alters the hemodynamics of the body.

Yeah.

And yet, the human body is so adaptable, so resilient, that it can completely neutralize this powerful drug in just 24 hours, simply by hiding away its sulfhydryl groups.

It's wild to think about.

It really is.

It's a stark reminder that in pharmacology, you aren't just pouring a chemical into a static test tube.

You are engaging in a dynamic, high -stakes negotiation with the body's own defense mechanisms.

So what does this all mean?

It means you now have the tools, the physics, and the pharmacology to completely master this material.

You understand the seesaw of oxygen supply and demand.

You know why nitrates dilate veins, while CCBs dilate arteries.

And you know exactly how to anticipate drug interactions to keep your patients safe.

We are so glad you joined us for this deep dive today.

From all of us here, thank you for listening, and good luck from the last -minute lecture team.

Best of luck on your exams, everyone.

Keep studying hard.