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Part 3 antihistamine tutorial | PharmacoPhoto | YouTubeToText
YouTube Transcript: Part 3 antihistamine tutorial
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Summary
Core Theme
Antihistamines, specifically first-generation ones that cross the blood-brain barrier, interact with histamine-1 receptors in the brain, impacting neurotransmission related to motion sickness, cognition, memory, and the sleep-wake cycle.
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okay so now that we've got that under
our belt the next thing that we need to
do is just take a little look at the
histamine one
receptor and the reason I say that
histamine one is because anti-histamines
work on the histamine one receptor
recall that there's a histamine 2
receptor it's the receptor in the
stomach in the parietal cells remember
in module one when we were talking about
the parietal cells there's uh in order
to secrete the acid the parietal cell
needs stimulation from a couple different
different
neurotransmitters but one of them is histamine
histamine
2 but we're not talking about the
histamine 2 receptor now it's the
histamine one receptor that we're
talking about and as we've seen that
histamine 1 receptor is in the periphery
but it's all also in the brain we also
have a histamine one receptor in the
brain it's a
neurotransmitter in the brain so it
doesn't do any of the things that
histamine does out in the periphery and
of course that's a really good thing you
know it doesn't do those things because
otherwise we'd have brain hemorrhages
and itchy
brain well obviously it it doesn't do
those things because first of all
histamine receptors in the brain are not
on the blood vessels in the brain and of
course the blood vessels in the brain
are tight junctions the the blood
vessels have tight junctions rather than
those loose Junctions that are necessary
for dilation and increased permeability
so we don't have that type of of uh
blood vessel in the brain and of course
uh histamine cannot actually cause an
itchy brain because there are no pain or
itch receptors in the brain so in the
brain it doesn't do any of the things
that it does out in the periphery in the
brain the only role is that of a
neurotransmitter but it's got two
different spots if you will uh of it's
two different responsibilities main
responsibilities as a
neurotransmitter so one of the primary
sites of histamine being used as a
neurotransmitter in the brain is at the
vomiting Center if you ever had motion
sickness it probably you know you
probably noticed that it didn't come on
immediately as soon as soon as the boat
started a rock you probably got a little
bit more and more nauseous for a while
and then finally started to vomit well
what what's happening there what's what
how is that happening well the
vestibular portion of the vestibular
cular nerve starts sending these
messages to the vomiting Center and the
way that the message is received is that the
the
histamine is one of those
neurotransmitters we'll discuss the
other neurotransmitter in just a minute
um but it's one of the two
neurotransmitters that is sending that
message it's basically the messenger
that says oh more and more um more and
more motion we're going to have to start
getting sick now it's one of the two
main neurotransmitters that are involved
are involved in that motion sickness so
given think about this right now and put
it on the chatboard what do you think an
ideal motion sickness medication would
be okay yes an antihistamine but exactly
what kind what kind of antihistamine
would be the best or would be the one
that would be useful yes yes one that
broke into the bloodb brain Barry and
what are those are those the first
generation or the second ones yes the
first generation
antihistamines the one that break into
the bloodb brain barrier and actually
have that antihistamine effect up there
at the between the vestibular cck
between the vestibular portion of the
vestibular cular nerve and the vomiting
Center so right there at that point
there's going to be the anti-histamine
is going to jump onto those receptors
and say nope histamine uh you
neurotransmitter don't get don't bind
onto these receptors and that of course
decreases the motion
sickness the ones that stay out in the
periphery are going to be pretty much no
use at all I mean there's a little tiny
bit that gets into the blood brain
barrier from even the second generation
antihistamines the one that the ones
that quote unquote stay out in the
periphery well there's a little bit of a
crossover into the brain very little not
enough to actually U be effective at
reducing the nausea and vomiting from motion
motion
sickness just by the way just remember
that there's four different Pathways
from for motion
sickness the uh the nausea and vomiting
from for instance uh when there's an
actual bug in the stomach when there's
something that is affect directly
affecting the nerves in the stomach or
intestines that's one pathway and then
there's another pathway that's in the uh
the toxic uh in the chemo receptor
trigger Zone there's another pathway
from the higher brain Center you know
the kind of nausea and vomiting that
that you feel oh you just see see a mold
carcus of something and just get sick to
your stomach well that's a different
pathway the only only type of vomiting
that is going to be addressed by our
first generation antihistamines is the
one from motion sickness also there's
kind of uh some other things that are if
there's problems in the inner ear then
that can be affected too so the one
place that we're going to find histamine
one in the brain is at that Junction
between the vestibular portion the
vestibular cular nerve and the vomiting Center
Center
but histamine also has a role in a
number of physiological functions in the
brain such as the sleep wake cycle and
it helps maintain arousal and it helps
maintain cognition and helps maintain
memory so if you were to inject an
anti-histamine or histamine into the
bloodb brain barrier just before an
examination which one are you going to
choose well I mean you know you probably
wouldn't choose either that's a silly
scenario but you'd want lots and lots of
histamine you would want histamine
before an examination what you don't
want to do is take an
anti-histamine before an important quiz
or examination okay because it affects
histamine affects and maintains arousal
cognition and
memory and the first generation
anti-histamines are going to break into
the bloodb brain barrier and affect all
of those okay so just using what we've
learned right here with respect to
histamine what histamine does in the
brain please answer this question what
are the side effects and the
contraindications of
anti-histamines that go into the bloodb
brain barrier and you might as well
start thinking about this one as well
what are the additional indicat ations
of antihistamines that go into the blood
brain barrier so so think of side
effects Contra
contraindications and additional
indications of just think about the
brain here just about what's happening
in the brain and what's happening with
histamine receptors in the brain and and
say you know what are the side effects
what would the side effects be you can
use the chatboard
no yep yep drowsiness yeah defin
drowsiness a decrease in memory yep a
decrease in in cognition
yep oh actually no we wouldn't call
reducing nausea a side effect it is one
of the effects that it reduces nausea
from motion sickness but it's we
wouldn't call it a side effect a side
effect is a secondary typically
undesirable effect of a drug or or
medical treatment so so that's a side
effect yeah we're getting used to those
terms still getting used to those terms
but we've identified the ones the main
ones so the main side effects are going
to be a decrease in cognition a decrease
in memory and you're going to be a bit
drowsy and given that what do you think
that the first generation antihistamines
like dyen hydramine would be indicated
for something else aside what it's used
for in the periphery what else would it
be indicated for can anybody think of
why you would want to be drowsy for
instance yeah so follow that
on y yeah insomnia it's indicated in
contraindications yeah one of the contra
most important contraindications is
driving heavy machinery so it's
contraindicated in people who operate
heavy machinery and it would also of
course be contraindicated in some
professions where the person would have
to be alert so something like air
traffic controllers or you know students
thing and now we're ready for sub
question three
so the sub question three is briefly
explain the side effects and
contraindications we remember what those
terms mean side effects and
contraindications of Dien hydramine uh
due to its crossing the brain and acting
on the histamine one receptors I'm going
to give you just a few minutes U for
those of you who are listening to this
on tape uh just U so you'll have to
actually stop your tape okay I'll
I I'll cut out the minutes that I'm
giving the students who are right
here okay so sub question three will go
something like well Mrs Meyers Dien
hydramine and other first generation
antihistamines easily cross into the
brain and there they act like
neurotransmitters on what we call the
histamine one receptors the histamine
one receptor is important as a
neurotransmitter that's involved in
memory cognition and the sleep wake
cycle so therefore those first
Generations the the one that you're
taking the Dien hyamine is going to
decrease cognition it's going to
decrease memory and make you drowsy so
since uh since they decrease cognition
and make you drowsy they're
contraindicated in people operating
heavy heavy machinery so really Mrs
Myers you shouldn't be driving when
you're on those
medications so you kind of get the idea
of what we're looking for on that one
and then what I'm going to do is I'm
going to jump over to sub question four
for a
minute and that sub question is briefly
explain the indications of dyen
hydramine that are due to its ability to
cross into the blood brain barrier and
remember that this is briefly explain
the indications so just saying that Dien
hydramine is indicated for this and this
because of the fact that it goes into
the blood brain barrier is not going to
get you hardly any marks it's that
explanation that's
important and I'd answer with something
to the effect of now Mrs Myers if you
ever did find yourself needing an
antihistamine and at the same time you
needed a little something to help you
sleep or if you were ever on a boat and
you needed a medication to decrease
motion sickness well you could use dyen
hyamine at that time because what dyen
hyamine does is it goes into the brain
and works at the vomiting Center so it
decreases the messages to tell you that
you're moving too much it it's a a
specific kind of nausea the one that
makes you you sick from motion so it's
good for that it's not a general
um anti nausea medication but it also
works in another portion of the brain
that's important in the sleep wake cycle
so that's why it's good for insomnia if
you have insomnia and allergies at the
same time it would be good
then okay so that is pretty much what you
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