Chapter 42: Drugs for the Treatment of Fungal Infections

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Welcome back to the Deep Dive.

Today we are opening up a chapter that I think a lot of medical students and even practicing clinicians tend to skim over until they absolutely have to

We are looking at chapter 42 of Brenner and Stevens Pharmacology's sixth edition.

The title is Deceptively Simple, Drugs for the Treatment of Fungal Infections.

It is.

It's one of those topics that seems straightforward until you actually have a patient in front of you.

We spend so much mental energy on antibiotics and bacteria that fungi can feel like an afterthought.

But as we're about to see, they're anything but simple.

That is exactly the vibe I got from the text.

But the mission for this Deep Dive is to flip that script.

We're going to navigate chapter 42 exactly as it is written.

We're going to take these complex pharmacological mechanisms, which are frankly surprisingly intricate, and translate them into concepts you can actually use.

We want to move from the textbook page to

the bedside logic.

And the stakes are high.

That's really the first thing we need to establish here.

Fungal infections aren't just about itchy feet.

They can be lethal.

Right.

And that brings me to the hook that grabbed me immediately in the introduction.

We talk about killing bacteria like it's a tactical strike.

But the text makes this chilling biological point.

Bunteria are prokaryotes.

They're like aliens compared to us.

But fungi, fungi are eukaryotes.

That is the fundamental problem of this entire field.

When you look at a fungal cell under a microscope, you see a nucleus.

You see mitochondria.

You see organelles.

You see a remarkably dangerously similar to a human cell.

Which means the kill switch for the fungus is often uncomfortably close to the kill switch for the patient.

Exactly.

In pharmacology, we call this the challenge of selective toxicity.

If you're designing a drug to kill a bacteria, you have plenty of targets that humans don't have, like the 30S ribosome or the peptidoglycan cell wall.

But if you're designing a drug to kill a fungus, you're hunting for very, very subtle differences.

The window for error is tiny.

So here's the roadmap for this session.

We are going to follow the architecture of chapter 42.

We'll start with section one, the nature of the enemy.

We need to understand the biology of these infections before we can kill them.

Then, section two, the strategy of attack.

We'll break down the mechanisms, how we exploit those tiny differences you just mentioned.

And finally, we will do a deep dive into the specific arsenals, the polyenies, the azoles, the ocanocandins, and the outliers.

It's a logical flow.

You can't understand the target.

Okay, let's meet the enemy.

Section one of our discussion is the nature of fungal infections.

The text starts by classifying the organisms themselves.

It seems we aren't just dealing with one type of germ.

No, not at all.

The kingdom fungi is vast.

Yeah.

But medically, the text groups them into three main buckets that students really need to recognize instantly.

First, you have the yeasts.

Okay.

These are the simple ones, single spherical cells that reproduce by budding.

Like the yeast we use for bread, but pathogenic.

Similar concept, yeah.

Then, distinct from yeast, you have the molds.

The molds, right.

These are multicellular organisms.

They grow these long branching filaments called hyphae.

If you've ever seen that fuzzy green or white growth on old bread or cheese in your fridge, you're looking at a mold colony.

And then there's the group that sounds like a sci -fi villain, the dimorphic organisms.

They're shapeshifters, and this is a crucial adaptation for survival.

These fungi can exist as a mold out in the environments, in the soil, at room temperature.

But when you inhale them and they hit body temperature, 37 degrees Celsius, they transform into yeasts.

They adapt to the host to survive and replicate.

That is terrifyingly clever.

Okay.

So the text moves from what they are to where they attack.

It lays out a geography of infection.

The first stop is the surface, superficial or mucocutaneous mycosis.

Right.

And these are the most common fungal infections on the planet.

They affect the skin, the hair, the nails, and the mucous membranes.

They're annoying, they're unsightly, but they usually are life -threatening.

The text spends a lot of time on a group called the dermatophytes.

It lists three genera we need to know.

Epidermophyton, microsporum, and trichophyton.

These are the molds that cause ringworm.

And the reason they live on the surface isn't random.

It's their diet.

They have a very specific nutritional requirement.

They eat us.

Specifically, they feed on keratin.

Keratin is that tough structural protein that makes up the outer layer of your skin, your hair shafts, and your fingernails.

These fungi have evolved enzymes called keratinases that allow them to digest that protein.

They are literally eating your armor.

The terminology here is something I found really helpful to decode.

The text uses the word tinea for everything.

Tinia pedis, tinia capitis.

It sounds technical, but it's actually descriptive.

It is.

Tinea is just Latin for a worm or moth.

Describe the appearance of the lesion.

You get that classic red ring with a clear center.

It looked like a worm has curled up under the skin.

Just to be clear for the listener, there is no worm.

Zero worms.

It is 100 % fungus.

Okay, good.

So let's run through the list and the text so we can get the vocabulary down.

Tinia pedis.

Athlete's foot.

Classic itchy, peeling skin between the toes.

Very common in locker rooms where it's warm and moist.

Tinia capitis.

Ringworm of the scalp.

This one attacks the hair shaft itself, often causing patches of baldness or broken hairs.

We'll actually talk about a case study involving this later on.

Okay.

Tinia corporis and tinia cruris.

Corporis is on the body.

The classic ringworm rash on the arm or torso.

Corus is the groin, better known as jock itch.

And the stubborn one.

Tinia ungrium or onychomycosis.

Nail infection.

And this is the hardest of the superficial infections to treat.

Because the fungus is embedded deep in that hard keratin plate of the nail, it is incredibly difficult for topical drugs to reach it.

Now, superficial infections aren't just dermatophytes.

The text highlights a major yeast player.

Candida albicans.

Yeah, Candida is a commensal organism for many of us.

It lives in our gut or mouth without causing trouble.

We give it an opening, an opportunity, and it takes over.

It causes oral candy diocese, which we call thrush, those white patches in the mouth.

It causes vaginal yeast infections.

It causes diaper rash in babies.

It loves those warm, moist environments.

It really does.

There was one other superficial yeast mentioned.

Malassezia furfur.

This is a distinct one.

It used to be called pititrasporum orbicular.

It causes a condition called tinia versicolor.

Oh, right.

If you've ever seen someone with splotchy patches or dark patches on their chest or back, that is often malassezia.

It interferes with melanin production.

It's also the culprit behind seborrheic dermatitis or dandruff and scaling on the face.

Okay, moving deeper, the text describes subcutaneous mycosis.

These are deeper.

They involve the dermis and subcutaneous tissue.

The key takeaway here is the mode of entry.

You don't catch this from a towel at the gym.

These are usually caused by traumatic implantation.

What does that mean?

You get pricked by a rose thorn or get a splinter contaminated with soil fungi.

The text lists conditions like chromomycosis and sporotrichosis.

Exactly.

Sporotrichosis is actually colloquially called Rose Gardner's disease because of that thorn prick transmission mechanism.

And finally, the most dangerous category, systemic mycosis.

This is where the mortality rates skyrockets.

These are infections of the internal organs, pneumonia in the lungs, septicemia in the blood, meningitis in the brain.

The pathogens here are the heavy hitters, aspergillus, blastomyces, candida, cassidiotis, cryptococcus, and histoplasma.

The text makes a really critical distinction here regarding the patient's status.

It seems like the terrain of the patient matters as much as the bug.

Oh, it matters more.

The text divides these into two groups.

You have the endemic pathogens like blastomyces or histoplasma.

These are they can infect healthy, immunocompetent people if they inhale enough spores.

But then you have the opportunists.

Right.

Aspergillus, candida, cryptococcus.

These organisms are predators of the weak.

They generally do not cause invasive disease in healthy people.

But in the immunocompromised, patients with HIV, patients with uncontrolled diabetes, patients undergoing chemotherapy or organ transplant recipients,

these fungi are lethal.

The text specifically notes the rise of aspergillus and fusarium in hematopoietic stem cell transplant recipients.

It's a paradox of modern medicine.

As we get better at treating cancer and performing transplants, we are creating a larger population of highly vulnerable people.

We're keeping the host alive, but leaving the door wide open for the fungi.

The immunosuppression required to keep a transplant from rejecting is exactly the environment these molds need to thrive.

That sets the stage perfectly.

We know the enemy is tough and we know they strike when defenses are down.

Now let's look at the pharmacology.

Section two, the strategy of attack.

This is where we solve the eukaryotic problem.

We established that penicillin and typical antibiotics are useless here because fungi don't have bacterial cell walls or ribosomes.

So according to Brenner and Stevens, what is the golden ticket?

What is the one thing we can target?

It comes down to a single molecule in the cell membrane.

It's a sterile.

Mammalian cells, our cells, use cholesterol to maintain membrane stability and fluidity.

Okay.

Fungal cells use a related but distinct molecule called ergosterol.

Ergosterol versus cholesterol.

That subtle chemical difference is the basis for the vast majority of our antifungal arsenal.

If we can target ergosterol or the making of ergosterol, we can hurt the fungus while sparing the human.

Mostly.

Mostly, yes.

The text refers to figure 42 .1, which visualizes the mechanisms of action.

I want to try to paint this picture for the listener.

Imagine you are looking at a cross section of a fungal cell.

On the very outside, you have a rigid cell wall.

Just inside that, you have the cell membrane and inside that, the cytoplasm and the nucleus.

Right.

It's like a fortress.

The wall is the outer stone fortification.

The membrane is the inner gate.

So let's look at the targets.

Target number one is membrane structure itself.

This is where the polyenes, like amphotericin B, operate.

Think of amphotericin B as a saboteur.

It doesn't inhibit an enzyme.

It binds directly to the ergosterol that is already sitting in the membrane.

When it binds, it aggregates and forms a physical porohole.

So it punctures the tire.

Effectively.

The membrane loses its integrity.

Potassium leaks out.

Magnesium leaks out.

Protons rush in.

The cell's internal chemistry collapses and it dies.

It's a bactericidal or fungicidal effect.

Okay.

Target number two is the production of that ergosterol.

The synthesis pathway.

Right.

This is an assembly line.

The fungus has to build ergosterol from scratch.

It starts with a precursor called squalene.

Squalene is converted into lanosterol and lanosterol is processed into ergosterol.

And we have different drugs that sabotage different workers on this line.

Correct.

The elatomines, like turbinifine, hit the very beginning.

They inhibit an enzyme called squalene epoxidase.

So squalene piles up.

Yes.

And squalene is actually toxic to the cell in high concentrations.

Plus you get no ergosterol.

So it's a double whammy of toxicity and deficiency.

Then we have the azoles, like fluconazole.

They hit the next major step.

They inhibit the enzyme 14 -alpha dimethylase.

This is a cytochrome P450 enzyme that converts lanosterol to ergosterol.

If you block this, the cell ends up with a membrane full of garbage

methylated sterols instead of ergosterol.

And the membrane becomes weak.

Exactly.

It stops functioning properly.

Okay.

Target number three is the cell wall.

Now this is interesting because humans don't have cell walls at all.

We just have membranes.

Which makes this an incredibly attractive target for safety.

The echonocandins, like caspofungin, work here.

They inhibit the synthesis of a sugar polymer called beta -1 -bil -3 -D -glucan.

Glucan is like the bricks of the wall.

More like the mortar or the rebar.

It provides structural integrity.

If you block glucan synthesis, the cell wall becomes flimsy.

It can't withstand osmotic pressure and the cell bursts.

And since humans don't have that.

Since humans lack this pathway entirely,

these drugs tend to be very, very safe.

Finally, target number four is inside the nucleus, nuclear division.

We have two main players here with totally different mechanisms.

First, flucidocene.

This is an anti -metabolite.

It mimics the building blocks of DNA and RNA.

The fungus takes it up, thinks it's food, and incorporates it into its genetic material.

This just jams up the machinery of protein synthesis.

And the second word?

Grizzofolvin.

This drug binds to microtubules.

Microtubules.

They're the cables that pull chromosomes apart when a cell divides.

Grizzofolvin freezes those cables.

The cell tries to divide mitosis but gets stuck in the middle and fails.

So to recap the strategy,

we can punch holes in the membrane with polyenies.

Right.

We can stop the membrane from being built with azoles or allelamines.

We can smash the outer wall with echinocandins.

Or we can freeze the genetic machinery with flucidocene or grizzofolvin.

That is the toolkit.

It's not as large as the antibacterial toolkit, but it covers the critical vulnerabilities.

Moving to section three.

The text presents table 32 .1, which classifies these drugs not just by mechanism but by clinical use.

It seems to draw a hard line between systemic and superficial.

It's the most practical way to organize your thinking.

I mean, if a patient is dying of fungal sepsis, you aren't going to reach for a topical cream.

You need to know which drugs can travel through the blood.

So for sessetched mycosis, the list is amphotericin B, the azoles, the echinocandins, and flucidocene.

Right.

These are drugs that can be injected or taken orally to reach high levels in the blood and organs.

And for superficial mycosis.

We have the topical azoles, the allelamines, grizzofolvin, and tone of tape.

The text also drops a note here about combination therapy.

It specifically mentions flucidocene.

Yes.

This is a rule of thumb we will definitely revisit.

Flucidocene is almost never used as a solo agent.

Resistance develops way too fast.

It's almost exclusively used as a plus one alongside amphotericin B.

Okay.

Good to know.

Let's go deep into the specific drugs.

Section four, the polyene antibiotics.

The text introduces these as the heavy artillery.

They are.

They're derived from bacteria, specifically the streptomycetaceae family.

Chemically, they are fascinating molecules.

They have a large lactone ring, a macrolide ring containing a series of conjugated double bonds.

That's why they are polyenes, many double bonds.

And the text says they are amphoteric.

Which means they act as both an acid and base.

But perhaps more importantly, they are amphipathic, meaning one side of the molecule loves water, hydrophilic, and the other side loves fat, lipophilic.

Which explains how they can slide into a cell membrane.

Exactly.

They are perfectly designed to insert themselves into that lipid bilayer.

The lipophilic side binds to the ergostral, and the hydrophilic side forms the channel that lets the ions leak out.

The protagonist here, or maybe the is amphotericin B.

The text calls it the standard for severe systemic infections.

But when you look at the pharmacokinetics in table 42 .2, this is not an easy drug to use.

Oh, it's a nightmare to administer.

First off, you can't take it as a pill.

The gut simply will not absorb it.

It has to be given intravenously as a colloidal suspension.

And does it get everywhere in the body?

It gets to most tissues.

But here's a major, major limitation.

It does not cross the blood -brain barrier well.

The text states that concentrations in the cerebrospinal fluid, CSF, are only 2 % to 3 % of the plasma levels.

Wait a second.

We use amphotericin B to treat fungal meningitis, right?

We do.

So if it doesn't get into the brain, why are we using it for brain infections?

That's a great question.

And it works for two reasons.

One, the fungus in the meninges, like cryptococcus, is so sensitive to it that even those tiny trace amounts are often enough to begin the killing process.

Okay.

And two, when the meninges are inflamed, which happens during infection, the barrier becomes a bit leakier.

But strictly speaking, its penetration is very poor.

The half -life is also weird.

The text describes it as biphasic.

Yeah.

That means it has two phases of leaving the body.

The initial half -life is about 24 hours.

So if you measure blood levels, they drop by half in a day.

But the drug gets stuck in the tissues, liver, spleen, kidneys.

It binds there and releases very, very slowly.

So the terminal half -life, the time to actually clear from your system, is 15 days.

15 days.

So it just lingers.

Now we have to talk about the side effects.

In the hospital, this drug has a nickname,

Amphoterebal.

It earns that name every single day.

It is arguably the most toxic antibiotic in a routine use.

When you hang that bag, you know the patient's going to suffer.

The text highlights nephrotoxicity kidney damage.

It says this occurs in 80 % of patients.

Think about that number, 80%.

Wow.

If you put a patient on Amphob,

you are almost guaranteeing some level of kidney injury.

It's not a question of if, but how bad.

Why?

What is the mechanism?

It goes right back to selective toxicity.

Amphotericin B prefers fungal or gastral,

but it will bind to human cholesterol if it has to.

And the cell membranes in the kidney tubules are rich in cholesterol.

The drug punches holes in the kidney cells just like it does in the fungus.

That is brutal.

It causes renal vasoconstriction, squeezing the blood flow to the kidney, and direct toxicity to the tubules.

And the clinical result, what does that look like?

Azotemia, which is the buildup of waste products like urea and specific electrolyte crashing.

You see hypokalemia, low potassium, and hypomagnesemia, low magnesium.

The kidneys just leak electrolytes.

So if you are the clinician, what are you doing?

You are checking labs every single day, every day.

You are hanging bags of potassium and magnesium to replace what is lost.

And you are pre -hydrating the patient with saline, called sodium loading, to try to protect the kidneys.

The text also mentions infusion -related toxicity.

Ah, the shake and bake.

As soon as the infusion starts, the patient gets fever, chills, muscle spasms, vomiting, headache.

It's caused by the release of inflammatory cytokines, specifically TNF -alpha and IL -1.

It looks like a rigorous flu.

Can we prevent it?

Or at least manage it?

We pre -treat.

We give acetaminophen, Tylenol, antihistamines, sometimes corticosteroids, and moperidine, to stop the shivering.

It makes it manageable, but it's still very unpleasant.

Given how toxic this is, science must have found a better way.

The text discusses lipid formulations.

This was a huge breakthrough in the 90s.

Drugs like ambosone, ablacet, and ampotec.

The idea is simple.

You package the toxic amphotericin B inside a lipid vehicle, like a microscopic fat bubble or liposome.

How does that save the kidneys?

When you inject these liposomes, they stay intact in the blood.

They don't interact with the kidney cells as much.

Instead, they are taken up by the reticulo -antithelial system, the liver and spleen, or they target the site of inflammation where the fungus is.

The fungus releases phospholepices enzymes that break down the lipid, releasing the drug right where it's needed.

So it's a targeted delivery system.

Exactly.

It keeps the peak concentration away from the delicate renal tissues.

The toxicity drops significantly.

The efficacy stays high.

The only downside is the cost.

They are much, much more expensive than the standard formulation.

Before we leave polyenies, there are two others listed.

Nistatin and natamycin.

These are the little siblings.

Same mechanism punching holes, but they are even more toxic than amphotericin.

You absolutely cannot give them IV.

They would kill the patient.

So we use them topically.

Right.

Nistatin is classic for swish and swallow.

If a patient has oral thrush, they swish the liquid around to coat the mouth and then swallow it.

It kills the fungus in the gut, but it isn't absorbed into the bloodstream so it's safe.

It's also used in creams for diaper rash.

And natamycin.

That's a eyedrop.

It's the only approved antifungal for ophthalmic use.

It binds to the corneal tissue and doesn't penetrate deeper, which is perfect for treating fungal keratitis caused by molds like fusarium.

Let's move to the next major class, section 5, azole derivatives.

This is the workhorse class of modern antifungal therapy.

While amphotericin is the nuclear option,

azoles are the precision strikes.

They are synthetic compounds.

Chemically, they're split into two groups based on how many nitrogen atoms are in the ring.

Imidazoles with two nitrogens and triazoles with three nitrogens.

Generally, the triazoles are the newer systemic ones.

Yes.

Imidazoles like ketoconazole or muconazole are mostly topical these days, while triazoles like fluconazole and voriconazole are systemic.

Okay, let's look at the pharmacokinetics.

Absorption seems to be a big topic here.

It is.

Most are absorbed well orally.

But there is a huge caveat the text calls the acidity factor.

Some of them, specifically ketoconazole and intraconazole, require an acidic environment in the stomach to be dissolved and absorbed.

So if a patient has heartburn?

If they are taking antacids, H2 blockers like Zantac or proton pump inhibitors like omeprazole, they will not absorb the antifungal.

The pH is too high.

Right, the stomach pH is too high.

You have to separate the doses or give the antifungal with an acidic drink like a cola.

That's a very practical tip.

Take this with a Coke.

What about the brain?

We said Amphobie is bad at crossing the barrier.

The azoles are generally poor at it too, with one massive exception, fluconazole.

Fluconazole penetrates the CSS beautifully.

It reaches levels that are 50 -90 % of what is in the blood.

That makes it the clear winner for meningitis.

Absolutely.

It is the standard for maintenance therapy in cryptococcal meningitis.

It gets right where it needs to go.

Now we need to talk about safety.

The text highlights a crucial drug interaction point.

If you are a student, put a star next to this.

This is the board question and the lawsuit prevention point.

Azoles inhibit the human liver enzyme CYP3A4.

We hear about CYP3A4 constantly.

Because it is the metabolic highway for about 50 % of all drugs on the market.

If you give a patient an azole, you are effectively putting up a roadblock on that highway.

You are shutting down the waste disposal system for their other medications.

Can you give us a concrete example?

Sure.

A patient is on warfarin, or coumadin, to prevent blood clots.

You give them some conazole for a yeast infection.

The fluconazole stops the breakdown of warfarin.

The warfarin levels in the blood spike.

The patient's blood becomes dangerously thin, and they could have a massive internal hemorrhage.

Or statins.

Same thing.

Statin levels rise, leading to muscle damage, rhabdomyolysis, or benzodiazepines.

The patient gets overly sedated.

You have to review the medication list religiously before prescribing an azole.

The text notes that fluconazole has the least affinity for these human enzymes compared to the others, but it's still a risk.

Correct.

Ketoconazole is the worst offender, which is why we rarely use it systemically anymore.

Fluconazole is cleaner, but it's not perfect.

One more safety note.

Pregnancy.

It's nuanced.

The FDA issued a warning.

Chronic high -dose fluconazole.

We're talking 400 -800 milligrams a day during the first trimester is category D.

What does that mean?

That means there is positive evidence of human -feel risk.

Specifically, skeletal and cardiac birth defects.

But for a simple yeast infection?

A single low -dose 150 milligrams is category C.

That means risk cannot be ruled out, but it is generally considered acceptable if the benefit outweighs the risk.

But you have to be careful and have that conversation with the patient.

Let's drill down into the specific profiles in section six.

Let's do a rapid -fire on the specific drugs.

What defines each one?

Let's start with the trichonazole.

Think geography.

It is the drug of choice for the endemic mycosis we talked about earlier.

Blast mycosis and histoplasmosis.

It's also used for nail fungus.

And remember the absorption rule.

The capsule needs food or acid.

The liquid solution does not.

Got it.

Fluconazole.

The go -to.

It covers Candida and Cryptococcus.

It is excreted unchanged in the urine, which makes it the only azole davos that is good for fungal urinary tract infections.

And of course the famous one -pill cure for vaginal yeast infections.

Voriconazole.

The text calls this second generation.

This is the upgrade.

It was developed to fill the gap for molds.

It is the drug of choice for invasive aspergillosis, replacing Amphotericin B.

It is potent.

But it has a very strange side -effect profile.

It does.

Visual disturbances.

About 30 % of patients experience this.

They report altered light perception, photophobia sensitivity to light,

and chromatopsia.

Chromatopsia.

I mean, seeing colors differently or vividly.

Like looking through a kaleidoscope.

A bit.

It usually happens about 30 minutes after a dose and fades.

It is reversible.

But you have to warn the patients so they don't panic.

Also, voriconazole is tough on the liver, so watch those hepatic enzymes.

Okay.

Posseconazole and isovuconazonium.

These are the salvage therapy drugs.

You use them when everything else fails.

They have the broadest spectrum covering the nightmares.

Mucormycosis, caused by rhizopis or mucor, and fusarium.

If you have a patient with mold eating their sinuses or lungs, and voriconazole isn't working, you reach for these.

And ketoconazole?

The old guard.

It was the first oralazole, but it inhibits human steroid synthesis.

It blocks testosterone and cortisol production.

That causes gynecomastia or breast growth in men and menstrual irregularities.

Oh, not great.

No.

Because of that and the liver toxicity, it's mostly retired to dandruff shampoos, like nizoral.

Finally, the topicalazoles.

Coltrimazole, muconazole.

These are your over -the -counter creams.

Athlete's foot, yeast infections, common stuff.

But there is a new one mentioned for toenails.

Afiniconazole, brand name Jublia.

This is interesting.

It's a topical triazole applied with a brush.

It's designed to penetrate the nail plate.

But, and this is important, look at the data in the text.

It says it cured 17 % of infections compared to 3 % for placebo.

17%.

That is modest.

Yeah, that's not exactly a home run.

No.

It's better than the alternative lacquers, but it requires applying it daily for 48 weeks.

That is a year of daily painting.

It's an option for mild cases or patients who can't take oral pills, but it's not a magic eraser.

Section 7 covers the allelamines.

We touched on their mechanism inhibiting squalene epoxidase.

The main character here is turbinofine or lamicelle.

Right, available as a cream or a pill.

The oral form is the gold standard for onychomycosis, nail fungus.

Why is it better than the azoles for nails?

Pharmacokinetics again.

Turbinofine is keratophilic.

It loves keratin.

It accumulates in the nail plate and stays there at fundicidal concentrations for weeks after you stop taking the pill.

It creates a reservoir in the nail.

But it's not a quick fix.

No, absolutely not.

You have to manage patient expectations.

You take the pill for six weeks for fingernails or 12 weeks for toenails.

But even when you finish the pills, the nail still looks gross.

Why?

Because the drug kills the fungus, but it doesn't repair the damage.

You have to wait for the healthy, uninfected nail to grow out from the base.

For a big toenail, that can take 9 to 12 months.

Generally very well tolerated.

Some GI upset, taste disturbance, dysjucia, and rare liver toxicity.

But compared to amphotericin, it's candy.

Okay, let's look at the newest major class.

Section 8.

The Akinocandins.

The text calls them semi -synthetic lipopeptides.

These are the wall breakers.

As we said, they target the enzyme beta -1 -DL3 -glucan synthase.

They stop the fungus from building its outer shell.

The prototype is caspifungin.

What is its spectrum?

What does it cover?

It is excellent against candida, including species like candida glabrata or candida crusae that are often resistant to azoles.

And it is effective against aspergillus.

What doesn't it kill?

It does not work against cryptococcus.

Why?

Cryptococcus is a yeast.

Shouldn't it have a cell wall?

It is, and it does, but its cell wall structure is different.

It relies less on that specific beta -1 -DL3 -glucan linkage, so the drug just bounces off.

It's a mechanistic mismatch.

Administration.

Hybe only.

These are large molecules.

The gut can't absorb them.

But the trade -off is tolerability.

This is the beauty of targeting the cell wall.

Humans don't have this target, so the side effects are minimal.

You might get a little fever, headache, or phlebitis, which is irritation at the injection site.

But you don't get the kidney failure of amphotericin or the drug interactions of the azoles.

The text mentions two others, mycofungin and anidulifungin.

They are very similar.

Mycofungin is often used for prophylaxis in transplant patients.

Anidulifungin is unique because it degrades chemically in the blood.

It doesn't need the liver or kidneys to clear it.

That makes it great for patients with organ failure who can't handle other drugs.

We're in the homestretch.

Section 9.

Other antifungal drugs.

These are the ones that don't fit into the main families.

First up, flucidacin.

This is a fascinating drug.

It is a Trojan horse or a pro drug.

How so?

Flucidacin itself is harmless.

It's inert.

But the fungal cell has a specific enzyme called cytosine deminase.

It takes the flucidacin inside and converts it into 5 -fluoracil or 5 -FU.

And 5 -FU is a chemotherapy drug.

Exactly.

It's a potent anti -cancer agent that halts DNA and RNA synthesis.

The beauty is that human cells do not have cytosine deminase.

We can't make the conversion.

So the fungus basically commits suicide by turning a harmless molecule into a poison.

But if it's so safe for us, why does the text list bone marrow suppression as a side effect?

Because nothing is perfect.

Bacteria in our gut do have the enzyme.

They convert a small amount of the drug into 5 -FU, which is then absorbed.

That trace amount of chemotherapy attacks are rapidly dividing cells, leading to anemia, leukopenia, low white cells, and thrombocytopenia, low platelets.

And the cardinal rule of flucidacin?

Never give it alone.

Fungi can mutate the permiss enzyme, the one that lets the drug in, or the deminase enzyme very quickly.

Resistance develops in days.

So we pair it.

Usually with amphotericin B.

The ampho -B punches holes in the membrane, which allows more flucidacin to flood into the cell.

It's a synergistic attack.

This combination is the gold standard for cryptococcal meningitis.

Next is grizafulvin.

The old school ringworm drug.

As we noted, it halts mitosis by binding microtubules.

There is a specific biohack for taking this drug.

You must take it with a high -fat meal.

It is extremely lipophilic.

If you take it with water, you just won't absorb it.

Eat it with a burger or ice cream.

The text mentions it deposits in keratin precursor cells.

This is why it takes so long to work.

It binds to the keratin that is currently being formed.

It doesn't clear the fungus from the hair that is already there.

It makes the new hair resistant to the fungus.

You have to wait for the old infected hair to be shed and replaced by the new drug -loaded hair.

That brings us to box 42 .1, the case study.

Let's look at this real -world application.

So we have a five -year -old boy.

He presents with patches of hair loss on the scalp, scaling, and swollen lymph nodes in the neck posterior cervical lymphadenopathy.

Diagnosis?

Tinea capitis.

Scalp ringworm.

The most common cause in North America is trichophyton tonsurans.

And the treatment in the case.

They prescribed grusofulvin, but note the duration.

Six to eight weeks.

You can't just put a cream on scalp ringworm because the fungus is down deep in the hair follicle where creams can't reach.

You need systemic treatment to load the new hair from the inside out.

Also, the text notes grusofulvin is a CYP inducer.

Opposite of these OLS, it speeds up the liver.

So it reduces the effectiveness of warfarin and, crucially, oral contraceptives.

You have to warn female patients that their birth control might fail while on this drug.

Two minor players to finish the list.

Cicloperox and Tolniftate.

Cicloperox is a nail lacquer, brand name Penlac.

It has a broad mechanism chelation of ions, DNA repair inhibition, used for mild nails.

Tolniftate is the classic tenactin, a fiocarbonate.

It inhibits schooling and epoxidase like turbinifine, but is much weaker.

Good for mild athlete's foot, useless for nails or scalp.

We have covered the map.

From the biology of the eukaryotic cell to the brute force of amphotericin and the precision of the azoles.

Let's synthesize this.

What are the big takeaways for the listener?

Takeaway one.

Respect the biology.

Fungi are eukaryotes.

That similarity to humans is the source of all the toxicity we discussed.

Takeaway two.

Know your targets.

Right.

Polyenies like MFOB punch holes in the membrane and you have to watch the kidneys.

Okay.

Azoles stop the assembly of the membrane.

You have to watch the drug interactions.

Echinocandins break the wall.

They're safe, but they're IV only.

And the lilamines like turbinifine are the nail specialists.

And takeaway three.

Context matters.

The drug you choose depends entirely on the patient.

Is it a healthy kid with ringworm or a transplant patient with invasive aspergillus?

Exactly.

And remember the review question from the end of the chapter.

Why is caspofungin the safest mechanism?

Because we don't have cell walls.

It's the closest thing to a magic bullet we have.

I want to leave the listener with a final thought to chew on.

We've listed a lot of drugs, but when you zoom out, we're really only hitting three or four targets.

Membrane, wall, DNA.

It highlights the fragility of our position.

We're seeing resistance rise.

Candida auris, a multidrug -resistant yeast, is spreading in hospitals globally.

As our population of immunocompromised patients grows, the fungi are adapting.

We are in an arms race.

And unlike with bacteria where we have dozens of classes of drugs, our antifungal quiver is relatively light.

It's a sobering reminder that while we have tools, the war is far from over.

It certainly isn't.

Thanks for listening to this deep dive into pharmacology.

This has been the Last Minute Lecture Team.

Good luck with your studies.