Absorption, was talking about the routes,
and it is the time from the route of entry
until it gets into the bloodstream.
Then distribution is the next 1
of the pharmacokinetic processes,
and that's the movement of the drug from
the bloodstream to the target cells.
So, if you look at…drugs have to cross the membrane.
Now, there's a pretty cool picture
there of you seeing the capillaries
and where they mix in the middle,
and you've got the veins.
But drugs cross membranes
either through the pores,
they can use an active transport system,
or they just directly penetrate the cells.
So, distribution is from the
bloodstream to the point of action,
the target site that we want the drug to work on.
So, what does it take to
have effective distribution?
Well, you have to have good blood flow.
Now, we have types of patients
that don't have good blood flow.
They may have like Raynaud syndrome and not
have good blood flow to their extremities.
They might be diabetic and
had macrovascular damage.
In addition to good blood flow, you want the
drug to be able to exit the vascular system.
So part of distribution is moving it
through the body in the bloodstream,
but then the drug has to get out of the
vascular system and to the target cell.
So we want the drug to be able to
easily exit the vascular system,
and then the drug has to enter the target cell.
Okay, so, let's go back and I just wanna
make sure that we're clear on that concept.
Absorption is from the site
of entry to the bloodstream.
Distribution is the bloodstream
to the target cell.
So you need the good blood flow, the drug needs
to be able to get out of the bloodstream,
and the drug needs to be able
to enter the target cell.
So, that's probably a pretty shocking
picture for you to take a look at.
We want to talk first about who
has challenges to distribution.
Now, I mentioned this before, but this
is a picture of a diabetic foot ulcer.
Here's the problem.
Diabetic clients often don't
have good feeling in their feet.
They might have pain or neuropathy,
or they might have total numbness.
So if they step on something and there
they get a cut or a sore on their foot,
and they don't do regular foot care,
they can often get an infection
that they're completely unaware of.
That's why we always recommend diabetic
clients to wear shoes around the house.
So if a client gets a wound on
their foot and it's not treated,
we need to then go in and
treat it with an antibiotic.
Well, we can give them an IV antibiotic.
That'll go in really quickly,
go through the bloodstream,
but trying to get it down to
that foot is problematic.
It's a distribution issue, because
we don't have the good vasculature
to deliver the antibiotic
to where the infection is.
And that's why diabetic foot ulcers
can get completely out of control.
The patient doesn't realize that they
have a wound, it becomes infected,
and then we have a really difficult time
of getting the medication
down to where we need it.
Abscesses don't have good blood supply.
So they have giant pockets
of pus in different places.
That's why a lot of times, those wounds
have to be incised and drained,
and then we can get the infection
taken care of with the antibiotic.
The last 1 is tumors.
Tumors don't have a good blood
supply right to the core,
so we have a hard time getting
chemotherapy to them.
And patients often require surgery
called debulking, where they go in
and make the tumor smaller, so that we
can get more medication to the tumor.
So, if distribution is moving from
the bloodstream to the target site,
we talked about people who
don't have good blood flow.
Diabetic foot ulcers, people have
abscesses because of giant pus pockets,
or people with tumors, because they have limited
blood supply to the core of that tumor.
Now let's talk about capillary beds.
Most of the capillary beds, they're pretty loose.
and the drugs can pass between the cells
and don't have to go
right through the cells.
So they've got these nice, big, open spaces…well,
relatively, because they are capillaries.
But they've got these nice, big, open spaces and
the drugs can pass right between the cells.
They don't have to go through them.
But there's a really special place in our
bodies in the central nervous system
where the capillaries form what
we call the blood-brain barrier.
Now, I have to say that slowly because my
tongue gets tied when I try to say it.
But the blood-brain barrier is a great
protective device, but can also be problematic.
Okay, the capillary junctions there are tight.
There are no gaps between these beds.
Most capillary beds, they really have nice, easy
spaces, and the drug can just go through there.
But the blood-brain barrier is different.
Super tight junctions, there's no
gaps like most of the other beds.
So the drugs have to pass through the cells
in the capillary bed instead of between them.
So that's why the blood-brain barrier is
able to keep out a lot of substances.
So, you've got this P-glycolprotein
thing, it's super cool,
because it'll actually pump blood back
into the bloodstream versus the brain;
another way that that blood
brain barrier protects the CNS,
the central nervous system,
from drugs entering it.
So, only lipid-soluble drugs
with a transport system
can actually cross the blood-brain barrier,
and we'll talk about which ones those are later.
But the purpose of the blood-brain
barrier is to protect us from toxins,
but it also protects us
from helpful medications.
So, say, you have a CNS infection
like meningitis or encephalitis,
we have a distribution problem
because of that blood-brain barrier.
There's a lot of antibiotics that
can't cross the blood-brain barrier.
So what you need to do is we found
some medications that actually will.
Cephalosporins 3rd, 4th, and 5th generation
will actually cross the blood-brain barrier,
where most of them do not.
So the blood-brain barrier is a good thing.
It protects toxins from getting to my
central nervous system, but remember,
it can also be problematic if I'm trying to get
a medication into my central nervous system.
It can be a problem with antibiotics,
in treating a CNS infection.
It can be a problem for people that
need more dopamine in their brain,
like Parkinson's patients.
We have to throw another drug
across the blood-brain barrier
that gets turned into the
dopamine that they need.
Special populations are at risk are newborns.
Newborns have immature blood-brain barriers,
so they can't keep toxins out as well, and
they can't keep CNS drugs out as well.
So they will allow bad things into the CNS.
So, as nurses, we need to know if it's a CNS drug,
it needs to be extreme caution that
we ever gave that to a newborn.
Okay, well, speaking of babies, how about let's
talk about the placenta and distribution.
So, we're not going to go into a lot of
detail on that here, but just keep in mind.
Anytime you have a female who is
pregnant, you want to make sure
that you're extra careful with
the medications that they give,
because the placenta is not
like the blood-brain barrier.
It does not prevent drugs
from circulating to the baby.
So, many of the drugs can
pass through the placenta,
is what you have to be very careful with
what drugs a pregnant woman would take.
Now, they used to be called categories,
and how the A, B, C, D and X was the one
everyone wanted to pay attention to.
Because category X drugs means you absolutely
do not give them to a pregnant woman
because the risk to the baby clearly
outweighed any benefit of the drugs.
Now we're changing to a different system.
It's being replaced with
what they call a narrative.
And what they found is that not all the
drugs that are on the category X list
really should be totally
forbidden to pregnant women.
So now they're giving much more
information, hence the name narratives.
They're giving more information
so that your healthcare provider
and you can make a more informed decision
and really weigh out if the risk to the baby
outweighed the potential benefits or not.
So it's just another way
you're gonna make a better
and informed decision about
drugs in the placenta.
Okay, so that's absorption.
Pause for a minute and see if you can think
through what is the definition of absorption.
Now take a minute and see if you can come up
with at least 6 different routes for absorption.
What's the definition of distribution?