81 – Crystallization and Solid Form Selection (S6E6)

Have you ever really thought about what goes
into that tiny pill you swung? I mean, it seems
pretty simple, right? A solid little chunk of
medicine. Well, yeah, you would think so. But
there's a whole world of fascinating science
happening at the molecular level. And it all
starts with something called crystallization.
That's right. And today, we're going to do a
deep dive into crystallization and solid form
selection. Exactly and to do this we're going
to pull from all sorts of sources like the really
in -depth stuff from pharmaceutical scientists
You know the hardcore chemistry and then also
some more general overviews of drug development
Yeah, it's amazing how much goes into just choosing
the right solid form of a drug. It's not just
making a solid, it's like a fundamental decision.
Fundamental decision, really? Oh yeah, it impacts
everything. Like how easy is that drug to handle?
How long it will last on the shelf? And most
importantly, how well it actually works inside
your body. So it's kind of like choosing the
right building blocks for the medicine. Yeah,
exactly. A good analogy, actually. So to kick
things off, let's talk about why this whole crystallization
thing is so important. OK, yeah, let's do that.
What makes it so important that a drug needs
to be in a specific solid state? Well, for a
drug to do its job, it usually needs to be absorbed
into your system, right? Right. And to reach
its target and do its thing. Like we see in the
process of new drug discovery and development,
absorption is really tied to the drug's properties
in its solid form, especially its ability to
dissolve. OK. So it's not just about getting
it into a solid form. It has to be the right
kind of solid form. Precisely. Think of it like
this. If a drug can't dissolve properly, it can't
get where it needs to go and, you know, won't
do much good. Even for injected drugs, they still
need to stay in solution to avoid causing problems.
So the drug has to dissolve properly at the right
time and the right place in the body. Yeah, exactly.
So even if a drug is injected, it still needs
to remain in a dissolved state at that injection
site. Gotcha. So then what about polymorphism?
I've heard that term before. How does that play
into all of this? Ah, polymorphism. Yeah. It's
pretty fascinating. Basically, it's the ability
of a drug to exist in more than one crystal form.
Oh, okay. So it's not just one solid form. There
could be multiple ones. Right. Think of it like
carbon. You've got diamond super hard, and then
you've got graphite. Like what's in your pencil?
Totally different. Totally. But they're both
made of carbon. Exactly. Same atoms, different
arrangement. And that's the same with these drug
crystals. Different arrangements mean different
properties. OK. So for a drug, that means? Different
properties mean different ways it behaves in
the body, like how easily it dissolves or how
stable it is on the shelf, all that jazz. So
different polymorphs, which is what these different
forms are called, can actually impact how well
the drug works. Big time. Even the same polymorph
can change over time. Like this research from
back in 1990 by Cinco, Yi, and Amidon, it showed
that a solid drug's ability to dissolve can actually
change as it ages. Well, hold on. So even if
you have the right form, it can still change
and maybe not work as well. That's a bit scary.
It is something to keep in mind. And it's discussed
in early drug development, bringing a preclinical
candidate to the clinic. And when you start with
different polymorphs from the get go, Well, those
differences in how fast they dissolve can be
even more dramatic. This is super important for
drugs taken orally because if it doesn't dissolve
well in your stomach, it might not get absorbed
properly. Exactly. It's like trying to make tea
with a tea bag that doesn't open. You're not
going to get a very strong brew. Uh -huh. I get
it. There was a study done in 2002 by Angst and
others. They looked at an antiretroviral drug.
It highlighted how a drug's solubility is affected
by its solid form and how that can interact with
how it's formulated and even whether you've eaten
or not. It's also talked about in early drug
development, bringing a pre -clinical candidate
to the clinic. Wow, so many factors to consider.
So how do scientists make sure they get the right
polymorph in the first place? Well, controlling
the crystallization process is key. As we saw
discussed in continuous manufacturing of pharmaceuticals,
using techniques like continuous crystallization
gives them much more control over which form
is produced. Makes sense. More control, less
chance of ending up with the wrong form. Now,
what about stability? How long a drug lasts on
the shelf matters too, right? Oh, absolutely.
The stability of a drug substance, both physically
and chemically, is a big deal. Okay, so we don't
want the drug to break down or change over time.
Right, because as... pre -clinical development
handbook ADME and biopharmaceutical properties,
explains if a drug degrades, it becomes less
effective and potentially unsafe. So keeping
that shelf life long is super important. But
how does this all tie back to crystallization
and the solid form? Well, the solid form you
choose can directly impact stability. You can
think of it like stacking boxes. A well -organized
stack is going to be much more stable than a
messy pile, right? Yeah, so a more ordered structure
is more stable. Makes sense. Exactly. And the
crystalline structure does just that. It creates
a more ordered, stable environment for those
drug molecules. And there are tons of examples
in the scientific literature where researchers
have found ways to make drugs more stable through
crystallization. Oh, really? Like what? Well,
imagine a scenario where they're working with
a drug that's not very stable. They might find
that a specific crystal form is way more resistant
to breaking down, so then they focus on tweaking
the crystallization process to produce that more
stable form consistently. So they're kind of
like fine -tuning the recipe to get the best
results. That's a great way to put it. They might
find that adjusting the acidity of the solution
or using a specific blend of solvents does the
trick. In some cases, they might even be able
to remove impurities during recrystallization
that could speed up degradation. And voila, a
more stable drug. That's incredible. So it's
clear that getting the right solid form is crucial,
but how does it affect turning that solid into
something we can actually take, like a pill or
a capsule? How do they formulate it? Great question.
The solid form of the drug basically dictates
what's possible when it comes to formulation.
Okay. As the process of new drug discovery and
development points out, those who formulate the
final medicine need to consider a lot of things,
like the drug's physical and chemical properties
and how it behaves in the body, you know, all
those details. Yeah. So solubility and dissolution,
which we've talked about and which are influenced
by the crystal form, are super important for
the formulator. Right, because they directly
impact bioavailability. Right. Yeah. Like how
much of the drug actually gets into our system.
Exactly. If a drug doesn't dissolve well, formulators
have to get creative. They might have to use
techniques like making nanosuspensions. It's
this cool thing where they create these teeny
tiny drug particles to boost the surface area,
which helps with dissolution. Wait, so they make
the particles super small so they dissolve better?
Yep, that's the idea. And there's some research
from 2001 by Muller, Jacobs, and Kaiser on this.
It's mentioned in early drug development, bringing
a preclinical candidate to the clinic. It's kind
of like grinding coffee beans the finer the grind
the stronger the coffee I see the analogy So
they're basically manipulating the physical properties
of the drug to overcome limitations caused by
the crystal form Precisely. And the scientific
literature is full of real -world examples of
this. Think about a situation where a drug keeps
forming big, stubborn crystals that don't want
to dissolve. They can tweak the crystallization
process to produce smaller particles instead.
You know, carefully controlling things like the
solvent they use and the speed at which it's
added. They might even use seed crystals to guide
the process. Seed crystals. Yeah, it's like giving
the crystal formation a blueprint to follow.
But the goal here is to avoid uncon... controlled
crystal formation, what's called secondary nucleation,
you want a nice consistent batch of particles
all roughly the same size. Got it. That makes
the formulation more predictable and reliable.
So we've talked a lot about the physical aspects,
but what about the chemistry involved in all
this? Ah, the chemistry. It's the foundation
of everything, really. Understanding the chemical
processes during crystallization is crucial for
controlling the solid form we end up with, by
manipulating things like temperature, solvents,
mixing speed, all that good stuff. It's like
they're conducting a microscopic orchestra, getting
everything in sync to produce the perfect crystal.
That's a great way to put it. And with techniques
like continuous crystallization, they have a
lot more control over these parameters. That
means they can consistently get high quality
crystals and effectively get rid of impurities.
It sounds very precise. Oh, it is. They even
use advanced techniques like seeding, which we
talked about before, adding small crystals of
the desired form to guide the growth. And they
use sensors that monitor the crystallization
in real time. This is called Process Analytical
Technology, or PAT for short. And all of this
helps them control what we call super saturation.
Super saturation. That sounds important. Oh,
it is. It's like the driving force behind crystallization.
Think of it as how much of the drug is dissolved
in the solution beyond its normal solubility
limit. The higher the supersaturation, the stronger
the push for the drug to come out of solution
and form crystals. So by carefully controlling
supersaturation, they can kind of steer the crystallization
process in the right direction. Exactly. And
you can find lots of examples in the literature
where scientists have used their knowledge of
chemistry to really fine tune this process. For
instance, there's a case where they use what's
called a two -phase system with a phase transfer
catalyst. This allows them to carry out a chemical
reaction in a more controlled manner, ultimately
helping them get the right solid intermediate,
which is a stepping stone to the final drug crystal.
So even the steps before crystallization are
influenced by this deep understanding of chemistry.
Absolutely. Everything is connected. There was
another case where they carefully control the
amount of a solvent called methanol and the temperature
during a reaction and then followed that with
crystallization. And by doing this, they were
able to produce a super pure and stable intermediate.
It's all about tweaking those chemical parameters
to get the best results. Fascinating. Even seemingly
small changes can have a ripple effect throughout
the whole process. For sure. And as we mentioned
earlier, with continuous crystallization, controlling
supersaturation isn't just about getting the
right crystal form. It's also about preventing
issues like agglomeration, which is when crystals
clump together, and particle breakage. Those
things can really mess with the final formulation.
Wow. So much complexity in something that seems
so simple. It's incredible how much science goes
into creating something like a pill. Right. And
it all starts with understanding crystallization
and solid form selection. It seems like we've
just scratched the surface here. Oh, definitely.
But hopefully... This deep dive has given you
a new appreciation for the hidden world of drug
development. Absolutely. We've seen that crystallization
is much more than just making a solid. It's a
fundamental process that shapes a drug's properties,
from its polymorphism and stability to how it
can ultimately be formulated into an effective
medicine. It really underscores the interconnectedness
of chemistry, solid state science, and formulation.
It's a beautiful dance of scientific disciplines
all working together to ensure that the medicines
we rely on actually work as intended. It's amazing
to think that every time we take a pill or a
capsule, we're benefiting from this intricate
process. Scientists have carefully selected a
specific crystal structure, often from numerous
possibilities, to ensure it dissolves at the
right time stays stable on the shelf, and ultimately
delivers its therapeutic benefit. It makes you
wonder what other hidden complexities are at
play in the medicines that keep us healthy. It's
something to ponder for sure. Well on that note,
we'll wrap up this deep dive. Thank you for joining
us as we explored the fascinating world of crystallization
and solid form selection. It's been a pleasure.
Always happy to talk shop. Until next time, stay
curious.