Azithromycin (S24E10)

Welcome to the Deep Dive. You're here because
you want to get smart fast. And today, we're
doing just that, focusing on azithromycin. That's
right, a really common antibiotic one many people
have probably encountered. Exactly. So we've
gone through a ton of material, scientific reviews,
market reports, clinical trial data, even patents.
All the good stuff. Our mission today, to really
unpack azithromycin, its history, how it works,
what it's used for, and its wider impact. Think
of it as the essential guide. We'll cover the
science, the story, and, well, some of the controversies,
too. OK, let's jump right in. The history. Where
did this drug actually come from? It wasn't like
an ancient discovery, right? No, no, not at all.
It's actually relatively modern, discovered in
the late 1970s. Oh, OK. Yeah, by a Croatian pharmaceutical
company called Pliva. But the interesting part
is, it wasn't built from scratch. How so? It's
what we call a semisynthetic derivative. It's
based on an older antibiotic, erythromycin A,
which had been around since the early 1950s.
Ah, so they were trying to improve on something
that already existed. Precisely. Erythromycin
worked, but it had some drawbacks. One big one
was instability in stomach acid, meaning it could
get broken down before your body fully absorbed
it. Right, less effective then. And it wasn't
quite as good against certain types of bacteria,
particularly some gram negatives. So pliva scientists
were looking for ways to tweak the erythromycin
molecule to overcome these limitations. Clever.
And they succeeded, obviously. They did. And
they were smart about it, too. They secured pretty
broad patent protection for their new compound,
azithromycin. Which turned out to be a very valuable
move, I imagine. Hugely valuable. Because in
1986, they struck a licensing deal with Pfizer.
Ah, Pfizer. That explains the global reach. Exactly.
Pfizer marketed it as Zikromax pretty much everywhere
except Central and Eastern Europe, where Pliva
kept the rights. That partnership really transformed
azithromycin from a promising discovery into
a, well, a blockbuster drug. It's a classic story
of innovation meeting market power. It really
is. Shows how both discovery and strategic business
decisions are needed to get important medicines
out there. Okay, so we know when and who. Let's
get into the how. How does azithromycin actually
fight off bacteria? What's the mechanism? Right.
So azithromycin is classified as a macrolide
antibiotic. Its main job is to stop bacteria
from making proteins. Proteins are essential
for bacteria, right? For growth and everything
else. Absolutely essential. Think of a bacterium
having a little factory inside it to build proteins.
Azithromycin jams up a key piece of that factory's
machinery. Which piece is that? It specifically
binds to something called the 50S ribosomal subunit.
By sticking there, it basically prevents the
factor from assembling proteins correctly. No
proteins, no growth, no multiplication. throwing
a wrench in the works. Exactly like that. It
doesn't usually kill the bacteria outright. It
mostly stops them from growing bacteriostatic,
we call it. Okay. Now, the sources mention cross
-resistance with erythromycin. What does that
mean for us? That's a really important point,
especially now. It means if bacteria figure out
a way to resist erythromycin, that same trick
often works against azithromycin too. Why is
that? Because they're so similar chemically,
and they target basically the same spot on that
ribosome. So a change the bacteria makes to protect
itself from one often protects it from the other.
It's a major issue with antibiotic resistance.
Got it. Something else that stood out was its
pharmacology, how it gets taken up by our own
cells, like white blood cells. Yes. This is one
of azithromycin's quite unique features. Its
chemical structure, this dual -based thing it
has, allows it to be actively transported into
certain human cells. fibroblasts, white blood
cells like phagocytes. And why is that useful?
Well, think about where infections happen. White
blood cells naturally travel to those sites to
fight the bacteria. So if the azithromycin hitches
a ride inside these white blood cells, it gets
delivered in high concentrations right to the
battlefield, so to speak, directly to where the
bacteria are causing problems. That's pretty
smart drug design or maybe a beneficial property
they discovered. It's certainly a key part of
its effectiveness and it's not just about killing
bacteria directly. What else does it do? There's
growing evidence for immunomodulatory effects.
It seems to be able to influence our immune system's
response. Like calming down inflammation. Exactly.
It can reduce the production of certain pro -inflammatory
signals, cytokines. This can be really helpful
in conditions like, say, lung infections where
excessive inflammation can actually cause more
damage. So it fights the bugs and helps manage
the body's reaction. A double whammy almost.
Sort of, yeah. It adds another layer to its therapeutic
benefit, especially in respiratory diseases.
Okay, that makes sense. So, with all that in
mind, what are the main things azithromycin...
actually prescribed for it. The list seems pretty
long. It is quite broad -spectrum. It's definitely
a go -to for a community -acquired pneumonia
CAP. Both oral and IV forms are used there. Okay.
Also, acute bacterial sinusitis is really nasty
sinus infections. Pharyngitis or tonsillitis
like strep throat, especially if someone can't
use penicillin or the other first -line options.
Right, as an alternative. Yes. and uncomplicated
skin infections. Then there's a whole range of
sexually transmitted infections. Ah, yes. That
comes up a lot. Definitely. For non -gonococcal
urethritis and cervicitis, often caused by chlamydia,
it's famous for that single one -gram dose. Super
convenient. One dose and done. For that specific
indication, yes. Makes adherence much easier.
For gonorrhea, it's a bit different now due to
resistance. It usually requires a higher single
dose, two grams, and it's almost always given
with another antibiotic, like ceftriaxone. Because
resistance is a big problem with gonorrhea. A
huge problem. Using two drugs helps combat that.
It's also used as a single dose for chandroid,
another type of genital ulcer disease. And I
saw something about mycobacterium avian complex,
MAC. Yes, that's important, especially for people
with compromised immune systems, like advanced
HIV. Azithromycin is used both for preventing
M .A .C. infection, usually a 1200 -milligram
dose once a week, and for treating active M .E
.C. infection, typically 600 -milligram daily,
as part of a multi -drug regimen. Wow. And even
eye drops. Yep, for bacterial conjunctivitis.
Azazite is a common brand name for the ophthalmic
solution. It really does cover a lot of ground.
It certainly does. Now, during the COVID -19
pandemic, azithromycin got a lot of attention,
didn't it? often mentioned with hydroxychloroquine.
It absolutely did. There were some early small
studies, often in vitro or observational, that
suggested it might have some antiviral activity
or could potentially help maybe synergistically
with hydroxychloroquine. But that didn't really
pan out in larger trials. Largely no. Subsequent,
much larger, well -controlled clinical trials
like the recovery trial in the UK or the action
trial for outpatients generally found no significant
clinical benefit for azithromycin in treating
COVID -19 patients, especially those who weren't
severely ill. So the initial hype didn't match
the rigorous evidence later on. That's a fair
summary. It highlights how science works. Initial
observations need to be tested robustly. There
was also some real -world data, like a study
from India mentioned, suggesting it helped with
upper respiratory symptoms over five days. But
that's different from proving in effect against
the virus itself. Right. And I see notes about
potential synergy with other antibiotics against
biofilms. That sounds interesting. Yeah, biofilms
are these slimy layers, bacteria form, making
them harder to treat. There's some research looking
if combining azizromycin with drugs like tiging
cyclane could be more effective against these
resistant structures. Still early days for some
of that, though. And off -label use in pediatric
ICUs, any major concerns there? Well, off -label
use always requires careful consideration. But
one study we saw indicated that in that specific
setting, it didn't seem to increase the risk
of serious adverse events compared to its approved
uses, but again, requires careful judgment by
the clinicians. OK, let's shift to how the body
handles it. Pharmacokinetics, pharmacodynamics.
You mentioned the long half life earlier. Right.
That's a key pharmacokinetic feature. Its half
life is quite long, which allows for that once
daily dosing and often shorter treatment courses,
like the famous three day or five day Z -pack.
Makes it easier for people to take all their
medicine. Definitely a plus for adherence. Another
key point is its distribution. Even though oral
bioavailability, the amount that actually gets
into your bloodstream when you take a pill, is
only around 38 % compared to IV. Which sounds
low. It is relatively low compared to some drugs.
But azithromycin has this fantastic ability to
penetrate tissues extensively. Concentrations
in tissues like lung tissue or those white blood
cells we talked about can be much, much higher
than the concentration just floating around in
your blood plasma. So it gets where it needs
to go, even if not all of it gets into the blood
initially. Exactly. That tissue concentration
is crucial for fighting infections located in
those tissues. As for getting rid of it, it's
primarily metabolized or processed by the liver
and then eliminated mainly through bile. into
the feces. Okay, so how do they actually make
this stuff? It's not like baking cookies, I assume.
Definitely not. Pharmaceutical manufacturing
is pretty complex. For drugs like erythromycin,
it's typically done using batch production. Batch
production, meaning they make it in large separate
loads. Precisely. It involves multiple chemical
reaction steps, starting usually from that erythromycin
A precursor. Then there are critical stages like
crystallization, where the drug forms into solid
crystals, and purification, often involving filtration
and washing, to get rid of impurities and isolate
the pure azithromycin. And the sources mentioned
that the chemical transformation from erythromycin
to azithromycin requires strong reaction conditions.
Yes, some of the chemical steps involved can
be quite harsh, maybe requiring specific temperatures,
pressures. or reactive chemicals. Controlling
these conditions precisely is vital for safety
and also for ensuring you get a good yield of
the desired product without too many unwanted
side products. Sounds like scaling that up from
a lab bench to giant factory vats would be a
challenge. It absolutely is. That's process chemistry
and chemical engineering. You need large, specialized
reactors, often stirred tanks. Some might need
vacuum systems. Then specific equipment for crystallization
to control the crystal size and shape, which
can affect how the drug dissolves later. and
robust filters like filter presses to separate
the solid drug from liquids. And they're always
trying to make the process faster and more efficient,
right? Constantly. Optimizing reaction times,
improving yields, minimizing waste, ensuring
consistent purity. That's the name of the game
in pharmaceutical manufacturing. It's a highly
regulated and controlled environment. Speaking
of regulated, let's talk about the regulatory
side and maybe some of the bumps in the road.
It got FDA approval for Lots of uses. Yes, it
went through the standard FDA approval process
for its various indications and dosage forms,
tablets, suspensions, IV injections. But then
generics came along. How did that change things?
Massively. Once Pliva's and Pfizer's patents
expired, other companies could get approval to
make generic azithromycin. To do that, they have
to demonstrate bioequivalence. Meaning they're
version X the same in the body as zithromax.
Essentially, yes. Same rate and extent of absorption.
They also have to show their inactive ingredients
are safe. The result was a dramatic drop in price
and a huge increase in access. Generics dominate
the market volume now. But it hasn't all been
smooth sailing. There have been safety concerns
raised, particularly about the heart. Yes, that's
been a significant point of discussion and ongoing
surveillance. Several large observational studies
and meta -analyses have suggested a potential
link between macrolide antibiotics, including
azithromycin, and a slightly increased risk of
cardiovascular events. Like what kind of events?
Primarily ventricular arrhythmias, irregular
heartbeats originating in the lower chambers
of the heart, and, in some studies, a small increased
risk of sudden cardiac death. or overall cardiovascular
death, particularly when compared to no antibiotic
or perhaps penicillin derivatives. Some data
also hinted at a slight increase in heart attack
risk. That sounds serious. Did regulators act
on this? Yes. The FDA, for example, issued a
drug safety communication back in 2013. They
highlighted a specific study published in the
New England Journal of Medicine that suggested
a higher risk of cardiovascular death in patients
taking a five -day course of azithromycin compared
to amoxicillin or no antibiotic. But they also
noted limitations with that study. They did.
It was an observational study, not a randomized
control trial, which means it can show associations
but can't definitively prove cause and effect.
It relied on death certificate data, which can
sometimes be inaccurate, and it focused on an
outpatient population. So there was context.
And this relates to the QT prolongation issue.
Exactly. Zithromycin, like other macrolides,
is known to have the potential to prolong the
QT interval on an electrocardiogram. Which is
a measure of the heart's electrical recharging
time. Correct. If that interval gets too long,
it can increase the risk of a dangerous arrhythmia
called torsitis de pointe. This risk is higher
in people who already have QT prolongation, low
potassium or magnesium levels, a slow heart rate,
or who are taking other drugs that also prolong
the QT interval. So doctors need to be aware
of patient risk factors. Absolutely. It's a known
risk that needs to be managed. There have also
been reports of other potential issues, like
hepatotoxicity, liver injury, though that seems
rare, and reports of infantile hypertrophic pyloric
stenosis, a stomach muscle thickening in newborns
treated very early in life, also possible worsening
of myasthenia gravis. And inevitably, antibiotic
resistance. The big one. Because azithromycin
has been used so widely, often very conveniently,
it has unfortunately driven the development of
resistance in many bacteria. We mentioned gonorrhea
earlier. Where else is resistance a concern?
It's a growing problem in streptococcus pneumonia,
a common cause in pneumonia and ear infections.
Also in mycoplasma genitalium, another STI, and
even in common bacteria causing respiratory infections.
It limits the drug's usefulness over time. The
COVID situation probably didn't help with lots
of potentially inappropriate use. Our sources
mention concerns from Italy, for instance, where
widespread azithromycin use during the pandemic,
often for a viral illness, might have accelerated
resistance development. It really emphasizes
the need for antibiotic stewardship using these
drugs only when necessary. And there are even
restrictions on using it in animals we eat. Yes,
off -label use in food -producing animals is
restricted in many places due to concerns about
drug residues getting into the food supply and
potentially contributing to resistance in bacteria
that could affect humans. Okay, let's look at
the money side. Zithromax was a monster hit for
Pfizer. Oh, absolutely. A true blockbuster. Peak
annual sales were somewhere around $2 billion
back in 2005. Huge numbers. But generics changed
that picture dramatically. Completely. Once generics
enter the market, branded Zithromax sales plummeted.
That's the typical life cycle. But the overall
market for Zithromycin remained huge, just shifted
to lower priced generics. So more accessible,
less profitable for the original maker. Pretty
much. Key players now include Pfizer still, but
also major generic companies like Teva Mylon,
now Viatris, Indian companies like Zytus, Cadilla,
Lupin, Chinese manufacturers. It's a global market.
Rising awareness of infections keeps the demand
strong. How does it stack up in terms of cost
effectiveness? It depends heavily on what you're
treating and what you're comparing it to. That
single dose regimen for chlamydia was often considered
very cost effective, mainly because you could
be pretty sure the patient took the full treatment
course, potentially avoiding complications and
further spread. For other infections, the comparisons
get more complex. And its impact goes beyond
just treating individual infections into public
health. Definitely. This is a really important
aspect. Azithromycin has been absolutely crucial
for global efforts against neglected tropical
diseases. Like trachoma. Yes, trachoma especially.
It's a leading cause of preventable blindness.
Mass drug administration programs, often involving
donations of azithromycin, like through the International
Trachoma Initiative, supported by Pfizer for
many years, using single dose therapy, have made
incredible progress towards eliminating trachoma
in many parts of the world. It's also used for
Yaw's eradication efforts. So its single dose
efficacy and availability have had a massive
global health impact. Unquestionably. It's also
been studied quite extensively actually for reducing
overall child mortality in high mortality settings
in Africa and Asia, given periodically to young
children. Some trials showed significant reductions
in death rates. Wow. That's huge. Shifting slightly,
what about its cultural impact? The Z -Pak is
almost a brand in itself. It really is. That
term became synonymous with a short, convenient
course of antibiotics. It represented ease of
use. But maybe too convenient. Did it contribute
to overuse? That's the concern many people raise.
The sheer convenience and widespread availability
might have lowered the threshold for prescribing
or requesting antibiotics. potentially for conditions
like colds or bronchitis where they wouldn't
help because those are usually viral. Leading
to that resistance problem we discuss. It's all
interconnected. Increased awareness of antibiotic
resistance is in part a consequence of the era
of widely used convenient antibiotics like azithromycin.
And when supplies run short, like the recent
issues in Germany affecting SDI treatment. Right,
I saw that. It really underscores how reliant
public health systems have become on having these
key antibiotics readily available. shortages
can have immediate serious consequences. So wrapping
this all up, it's been quite a journey for azithromycin.
Absolutely, from an innovative improvement on
an older drug, becoming this incredibly widely
used tool for everything from common infections
to major global health campaigns. But also facing
significant challenges, the heart risks, the
ever -growing threat of resistance. It truly
exemplifies the double -edged sword of powerful
antibiotics, an amazing tool. but one whose effectiveness
we constantly risk losing if we're not careful.
Its story really forces us to think about how
we develop, use, and protect these vital medicines.
It does. The benefits have been immense, but
the challenges are real and demand ongoing attention.
Which leads us to a final thought for you, our
listeners. Considering this rise of resistance,
not just for azithromycin, but across the board,
how do we strike that critical balance? How do
we ensure access to life -saving antibiotics
while simultaneously preserving their power for
the future? It's not just a question for scientists
or doctors, but for all of us, something to really
mull over. Thanks for joining us on this deep
dive.