What is dynamic equilibrium? Well dynamic equilibrium is a concept that helps us
to understand the right amount of drug that needs to be administered in order
to reach a therapeutic level in a patient's body and it takes into
consideration all the concepts of pharmacokinetics, how a medication moves
through the body. So we are going to look at that and discuss a little bit more
about how that impacts us when we provide care right after this. Welcome
back my name is Tammy and this is NurseMinder and on this channel we do
everything nursing so if you're new here consider subscribing below so that you
get the next video when it's released. Did you know that when you take 500
milligrams of acetaminophen your body doesn't actually receive and use 500
milligrams? Well that's something that we call dynamic equilibrium. Now the
critical concentration of a drug is determined by all the factors we're
going to talk to today and that essentially says how much drug do I need
to cause a therapeutic effect. So I may be taking 500 milligrams of a medication
but I'm not actually utilizing 500 milligrams of a medication and this, the
actual number that a person can use from that dose will depend upon the four
factors we're gonna talk about next. When it comes to dynamic equilibrium one of
the first things we do is we have to actually take the medication so it needs
to be absorbed we can put creams on our skin, we can take medications orally, we
can insert them into the holes and the orifices of the body,
there's also sprays that we can inhale and injections as well. Multiple ways in
which we can get medications into the body in order for the body to start to
break it down and to absorb it. The route certainly will impact the rate of
absorption but also the patients conditions that may also be existing in
conjunction with the illness or injury that were being that we're treating. So
some of the barriers to absorption many of our drugs are taken orally, they have
been studied in healthy individuals, which is an important criteria, so for
example when we take an oral medication so maybe you've got a headache
or you've got some aches and pains and you take an ibuprofen or acetaminophen
we take those pills orally and they go into the stomach and it's the stomach
acid that starts to break down that food and it's needed in order stopping acid
that starts to break down that medication but if a patient is missing
stomach acid so for example maybe they're taking a proton pump inhibitor
because they have what's known as a GERD, gastroesophageal reflux, or heartburn is
what a lot of people call it, they may be missing that acid and so then we can
supplement that by giving them a couple ounces of coca-cola take your
medications with coca-cola if you're on a proton pump inhibitor because it will
help to break down that medication. Other times there's medications where you
don't want to have an acidic environment and this is where you see instructions
such as take with milk or protein and it decreases out acidic environment and it
increases the amount of drug that can be broken down. Another barrier might be
that the food can bind to that medication blocking its absorption. So
for those medications that's where you're going to see instructions such as
take before or after meals or on an empty stomach.
So those absorb shouldn't have to deal with how that medication reaches the
circulation and the tissues, distribution is how it moves into the body's tissues.
Okay. So imagine like an Amazon package has arrived at your door maybe it's come
by plane, train, foot, bicycle, somehow it has reached the circulation reached your
front doorstep and now we need to get it in to the door to the person who is
actually waiting for that package. So distribution is movement
into the body's tissues. One of the biggest things that impacts this is
whether the drug is water soluble or lipid soluble, The ionization of it and
the tissue perfusion. Okay so if you're office happens to be at the
very end of the building and nobody ever walks back there nobody's gonna bring
you your package because it's too far to go. So if we have poor tissue perfusion
there's no blood flow to that area the medication is not going to reach it. So
if you have an infection, say yeah classic case is diabetes who have already
decreased peripheral circulation as one of their potential complications, and now
they've got a wound on their toe, well I may give an antibiotic but it's not
going to reach the site because there's decreased perfusion, there's no traffic
heading there. Some drugs require proteins to bind to it now protein is
kind of like a transport mechanism maybe your amazon package was too big for
someone to carry by itself so they had to grab a cart to put it on and I
consider that to be like the protein that binds on to that medication
molecule. This becomes a larger transport mechanism and then it's not capable of
crossing over that blood-brain barrier and nor is it able to enter into the
small capillaries so what happens is as it reaches its destination the molecule,
the protein must unbind from that medication, looks like I have to take
that Amazon package out of my cart to deliver it to you. So medications must be
freed from the protein binding at the site of the tissue that it wants to
enter. The rate of release from this protein is part of what gives us our
slow acting and long acting information about medication. So if it's released in
a very slow fashion it's considered a long-acting and if it's released quickly
you know drive by move out you go, consider it fast acting. Lipid solubility
as I mentioned is, are the types of drugs that can cross the blood-brain barrier.
If it's water soluble it cannot cross that blood-brain barrier so lipid
solubility is a critical factor in order to get medications
the brain if that's where you have infection or swelling or disease process.
Medications do readily cross over the placenta and into the breast milk so
that is not an issue here so much with distribution in terms of being protein
bound or lipid soluble, they cross over quite naturally. The third element of
dynamic equilibrium is metabolism, So this is where the body takes those
foreign chemicals and breaks them down into active and inactive forms. The
inactive forms will be excreted and the active forms will further their journey
to their site of, or their target tissues to have an effect. The liver is one of
the major organs in which medications are metabolized and broken down. So what
happens when we take oral medications in particular we have this thing called
first pass effect. So if you recall from your circulatory system when
electrolytes, fluids and everything is absorbed from the small intestine it
enters into that portal circulation so what that means is when I take an oral
medication, remember goes into the stomach the acid starts to break it down
but most like about 60% of our drugs are absorbed in the small intestine so
they're drawn out of the lumen of the intestine into the circulation system.
They enter into the portal vein system which feeds the liver first. So what
happens when it gets to the liver is called first pass effect. The medication
reaches the liver, the liver transforms it active or inactive,
the inactive is destroyed and excreted and the activated form which actually
happens to require an enzyme called p450 then breaks it down and sends it to the
target tissues site to have its desired effect. So again going back to that
acetaminophen my headache goes away. What's really interesting to note here
is that the cytochrome p450 enzyme system actually once it's activated can
speed up the metabolism of other medications so this is where some of our
information comes from in terms of do not give this medication
with XY and Z because we may end up having either toxic levels or sub toxic
levels, sub-therapeutic levels of medications when they're given jointly.
Now because the liver is an important organ in terms of metabolism
it is a significant - you need to know the status of your patients liver
functioning in order to determine whether or not the dosage of the
medication needs to be increased or decreased. Similarly when it comes to
excretion, if our kidneys aren't working we can have a toxic buildup of
medications and that's related to the half-life and we'll talk about that in
one second. So excretion we get rid of our medications predominantly through
the urine but there are other places in which we can rid these toxins from the
body so for example saliva, our breathing, our lungs, in our feces, in our bile. Those
are also places where the body will excrete medications that are not active
or needed in the body. This takes us to the concept of half-life. Half-life is
the time it takes the amount of drug to go from one concentration to half of
that concentration and subsequently each time it goes down further so as an
example if I take 500 milligrams of medication at 8 o'clock and it has a
half-life of two hours then by 10 o'clock it will go down to 250
milligrams available. In another two hours we're looking at the time it takes
for 250 to reduce to half so by 12 o'clock that would reduce to 125. In
another two hours 125 becomes sixty seven point five milligrams and so on
and so on and so on. So you can see that a 500 milligram dose with a half-life of
two hours there is still medication in the system at midnight of that same day
but it's not a therapeutic level so what we tend to do is four half-lives;
we used for half-lives as a general rule for the next subsequent
dose. So if this was a medication that a two hour half-life
I would give it at eight o'clock and four half-lives later at two o'clock I would
schedule it again and then again four hours later I would schedule another
dose and that's to make sure that the body always maintains its therapeutic
level. The time to clear a drug from the body is very different than the time and
scheduling of frequency of medication admin. Of course there's several human
factors that can also affect dynamic equilibrium. We're gonna burn through a
few of those now just to give you a sense of how complicated medication admin
can be for your patient to make sure they're getting the desired effect
we want so desperately want. Wait we know that most drugs dosing is based on a
healthy 150 pound person so that means someone who is more than or less than
will require an adjustment in their medications. We know that age will impact
because we have pediatric doses geriatric doses. The gender men have more
muscle and so that if you give an injection is more rapidly absorbed, women have more
fat gosh I wish that wasn't true but it is women have more fasiqun slow
absorption. Physiological factors such as your hydration status, your electrolyte and
acid-base balance will influence how that medication interacts in the body.
Pathological meaning our disease processes so if I have liver or kidney
disease what is that doing to my metabolism my excretion. If I am taking
that proton pump inhibitor how is that impacting absorption. Psychological. We
certainly have heard the placebo effect where there is no maybe evidence of the
medication works as the person is experiencing it. So there is some
psychological element to the human factors of med admin Genetics we know
that not everyone responds the same. Immunological why do some people have
allergies and others don't why do some people seroconvert with their
hepatitis immunization and why do others not. Environment this is a really common one
for our our patients who go south for the winter that they will find that they
need to have their medications adjusted for the different
temperatures. Interactions what else are they taking is this food, grapefruit juices,
one of them is a herbal remedy over-the-counter natural remedy like
ginkgo biloba. Those are things that will interact with medications. Patient's
tolerance to that medication as well. So as you can see there's a several human
factors that also impact dynamic equilibrium. So dynamic equilibrium Wow
what a massive topic and a lot of things to consider when we give our medications
to patients. So it's not as simple as matching the medication to the package
that you have it's about looking at your patient in totality. So in this video we
have covered a lot of information, valuable information. We have looked at
pharmacokinetics specifically and the concept of dynamic equilibrium. We were
looking at absorption, distribution, metabolism, and excretion of medications
throughout the body. In addition we've looked at several elements of each
unique individual that you're caring for that might influence that critical
concentration and the therapeutic effect of the medication we so wish to have.
Until next time make it a great day :)