Okay, so we've done cardiovascular, we've done respiratory, we've looked at renal,
now we're gonna wrap up with GI as far as the physiological changes during pregnancy.
So unfortunately in pregnancy,
GI reflex and nausea and vomiting just kinda come along with it for some women.
It could be mild to a major and extensive but for most pregnant women,
delayed gastric emptying is a common theme.
So because they have delayed gastric emptying and they have prolonged transit time in the small bowel,
you can have increases in gastric pH and reduced gastric motility.
So we'll be looking at these things, you've got delayed gastric emptying
so it takes longer for your stomach to move that food through.
It's moving slower in the small bowel that's why you have a longer transit time
than they would've before they're pregnant.
Also you have an increase in the gastric pH meaning it's less acidic, right?
You have an increase so it's less acidic and your gut is just not moving a gastric motility.
So let's look at what difference that makes for your patients.
Because of the delayed gastric emptying and prolonged transit time,
it can alter the amount of an oral drugs that are available in the body.
Now why just oral drugs? Because we're talking about the GI system, right?
So oral drugs have to go in the mouth, down the esophagus,
to the stomach that's why they're impacted by gastric emptying
and the time in the small bowel. If it's an IV medication, it's not affected by those routes.
If it's an inhaled medication, it's going right to the lungs not having to deal with the stomach.
Now the increasing gastric pH and reduced gastric motility
can also reduce or delay absorption of the drug.
So like how we say can, might, alter, it really depends on the drug in the patient's body.
You need to be aware that these are things we consider but also keep in mind,
everyone is unique so we're gonna have to look at how the drug responds in their particular body.
Now I've talked about nausea and vomiting and their gut kinda slowing down
but now I wanna talk about metabolism and the liver.
Because the cytochrome P450, that's a group of enzymes,
they're super cool, interfere with lots of drugs.
Make them better, make them different, so they're highly involved in a lot of metabolism of drugs.
Some of the enzymes are increased and other enzymes are decreased
and when I say that, I mean the activity of specific enzymes.
Again, list them for you here because that's not really,
at this point, we're through time to memorize except to know the metabolism of some drugs
that are dependent on the cytochrome P450 in the liver,
they're gonna be increased faster so they might be metabolized faster
or they might be metabolized slower
because individual enzymes, specific ones, have increased activity and decreased activity.
So just keep that in mind.
Now let's look at pharmacokinetics.
Absorption, distribution, metabolism, and excretion.
There's really not a major effect in drug absorption but there is reduced gastric emptying, right?
And that small bowel motility.
So keep that in mind with pregnancy but overall, for the most part, there's not a major,
hugely significant impact on absorption.
Now, it will delay the medication making it to the plasma from oral drugs
but especially this is during labor.
So I have a patient in labor and they're taking oral medication.
That's when I'm probably gonna see the most significant effect in regards to absorption.
Now absorption, we're talking about oral meds.
Now in this green box, we're talking about intramuscular site.
So everything we just talked about was about an oral medication.
We already knew that the gastric motility is last and small bowel we've got that
but it doesn't have really super significant effects on it and unless they're in labor,
that has a more significant effect.
Now an intramuscular dosage, that's a little different, right?
We're talking about a different route.
So now we're talking about IM. Now, it's likely not impaired because tissue perfusion is increased, right?
Because you've got all this vasodilation, the heart's pumping harder, the lungs, kidneys,
everything's working harder so we're probably not gonna have an issue
with the absorption from intramuscular.
We don't give a lot of medications intramuscular
but if you had to, that's not really a concern in regards to absorption.
So looking at these in order, we've completed absorption.
Now we're gonna look at distribution.
Well, distribution is impacted by the increase in total body water in a pregnant woman.
Because we have increase in total body water,
there's a larger space with which in the water-soluble drugs distribute.
Remember, unbound drug is free to distribute.
Increased total body water, we've got a larger space with -- between these water soluble drugs distribute.
Okay, so you've got that point down.
Remember what happens though with extra total body water.
What happens to the serum albumin?
Well, because of this hemodilution, the extra total body water, the plasma albumin declines.
So when you're thinking about distribution,
extra total body water has a bigger space for water soluble drugs
but only have less plasma albumin,
it can cause increased free concentration of drugs that bind to albumin.
So unbound drugs are free drugs so with lower albumin,
we have increased free concentration of drugs that normally bind to albumin.
First point, talks about water soluble drugs with the extra body water.
The next point talks about with less plasma albumin,
we'll have increased free concentration of drugs that normally bind to albumin.
So we looked at absorption, distribution, and now clearly we're on to metabolism.
Now here's a key point. Hepatic metabolism increases but not the blood flow to the liver.
Okay? So metabolism is up but not blood flow.
So that's gonna impact drugs in different ways.
Drugs that are metabolized by the liver, remember it increases,
that's gonna be the impact of those drugs.
So there's an increased clearance of those drugs and I've looked at some examples for you there.
So hepatic metabolism increases but there's no increase in the blood flow to the liver
like there is to the kidneys in pregnancy.
So drugs that are rapidly metabolized, that their elimination rate
depends on how they're delivered to the liver, i.e. the hepatic blood flow,
they have an unaltered clearance.
Okay, so 2 things we talk about the liver: increased metabolism but not increased blood flow.
So drugs that are metabolized by the liver have an increased clearance
but drugs that their rate depends on how quickly it's delivered to the liver,
there's not an impact. That summarizes metabolism.
Before we go on, pause for just a minute and make sure those 2 points
are very apparent to you in your own understanding.
Is it delivery to the liver or is it dealt with right in the liver.
Now lastly it's excretion.
You know that there is a rapid loss of drugs that are excreted by the kidneys.
Why? Remember how the kidneys are all ramped up.
Now you think about a drug like amoxicillin.
That's a very common penicillin family-type antibiotic.
Now the dose should be doubled for systemic infections.
Why? Because amoxicillin is an example of this drug that there's rapid loss
because this is a type of drug that's excreted by the kidneys.
So in pregnancy, you may see a dose that is double for a systemic infection
but not for a UTI because penicillins are highly concentrated in the urine.
So if there's a systemic infection and we're using amoxicillin,
you'll see some unusually large doses for a pregnant patient in comparison
to a patient who's not pregnant.