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let's move on to the motility disorders
so the motility disorders can be treated
by several agents you have the dopamine
antagonists the motel and agonists the
laxatives and the anti diarrheal agents
let's start off with the : o mimetics so
: o mimetics lower the sphincter tone of
the lower esophageal sphincter now in
the past we use drugs like pathetic halt
but not anymore because pathetic all
tends to be a toxic agent and and
doesn't really work as well as we had
hoped
neostigmine which is an acetylcholine as
in have in acetylcholine has inhibitor
is often used in the hospital for acute
bowel distension now for further
information on this particular agent I
encourage you to take a look at our
autonomic nervous system pharmacology
lectures you'll have a much better
discussion about this particular drug in
that lecture other agents include the
dopamine receptor antagonist
specifically the d2 receptors so
metoclopramide is your prototypical
example of this it causes d2 blockade
and this causes increased bowel transit
so things move a little bit quicker they
may also cause parkinsonian symptoms so
you have to be fairly careful with these
agents they work also in the area of a
streamer which is part of the emetic
center of the brain and that for that
reason it's a very effective antiemetic
in surgery and in cancer patients
domperidone is another example of these
type of agents it does not cross the
blood-brain barrier so it makes it a
little bit different from metoclopramide
and it's therefore less likely to cause
CNS effects not surprisingly the
antiemetic effects of domperidone are
really not that significant now motele
and receptor agonists are an interesting
group because the prototypical agent is
actually an antibiotic erythromycin it
directly stimulates motel and receptors
and has benefits in patients with
gastroparesis now this also explains the
common cause common side effect of
diarrhea
erythromycin is hard on the system and
most patients who take erythromycin for
an infection complain of diarrhea and
that's because of direct motile and
receptor agonist activity let's take a
look at the laxatives now laxatives can
work in several different ways they can
be bulk forming so the classic example
of that is Salem now sigh ileum is a
seed and in order for it to work
properly it has to be chewed and not
just chewed but what we call masticated
and what we mean by that is that it has
to be chewed and mixed with saliva
because the salivary amylase will mix
with the sium and activate it now there
are over-the-counter agents that are
ground-up sigh helium they come as a as
an orange kind of a powder that you can
spread on your eggs or mix with your
orange juice those are actually quite
effective
over-the-counter agents such as
Metamucil contain sigh ileum that has
been activated now your herbalist
naturopath type people like to give
Salem seeds directly and that's fine
works really well as long as they chew
it and masticate it and mix it with
their saliva before they swallow it's
gross so I don't know why you'd ever
want to choose to do that instead of
just take Metamucil there are stool
softening agents docusate sodium is a
very commonly used agent I use it in
probably 60% of my patients over the age
of 80 glycerine tablets and glycerin
suppositories and mineral oil is also
another way of softening stool now
osmotic Karthik's work by actually
causing more water to be present in the
stool so it's kind of like creating a
gel matrix within the stool itself so
that water stays in the stool and that
the stool is softer magnesium oxide and
all of these other ones are examples of
that now
stimulants act by actually irritating
the bowel the prototypical and very old
example of that is castor oil I'm sure
you saw that on Bugs Bunny when you know
they gave the coyote some stimulant and
he had to go to the bathroom really
quickly at least that's how I remember
Castro it's not used anymore
we now use things like aloe and Senna
which are probably more gentle
and and easier on the system chloride
channel activators are less used at this
point in time how they work is by
increasing fluid bulk within the stool
itself and finally the opioid receptor
antagonists are an interesting way of
treating treating patients what happens
is is that we know that opioids are
constipating by blocking the opioid
receptor we believe that this will
reduce constipation particularly in
those patients who are on opioids so
there you have the list of the laxatives
have a look at this we're going to
present this slide to you as a
downloadable slide so that you can have
this in your own slide library let's
take a look at some of these other
agents now we to you before about
opioids being constipating we can
actually use opioids as anti diarrheal
agents as well and that seems logical
because opioids are constipating in and
of themselves however we don't want to
use strong lock the opioids and we
actually have an agent that is a weak
opioid it's commonly sold as imodium
it's a analog of meperidine it has a
minimal central nervous system effects
and maximum GI effects originally when
this agent was released on the market we
thought we would be using it for pain
control and the GI effects were so bad
that people complained about it but some
enterprising scientist at the drug
company said well why don't we use it
for diarrhea and actually it works
really well
so imodium is probably the number one
selling over-the-counter agent for the
use in anti diarrheal treatment other
anti diarrheal agents include Kalyan so
Kalyan is a naturally found magnesium
aluminum silicon and it's hydrated so it
works quite well pectin is an
indigestible carbohydrate that comes
from Apple's now the interesting thing
about pectin is that it actually absorbs
bacterial toxins and some fluids so when
you combine kalyan and pectin you come
up with an agent
called kaopectate which is sold
commercially now this agent can of
course cause constipation but when
you're giving a patient with diarrhea
this agent it works quite nicely now the
problem with kaopectate is because it's
one of these binders that binds toxin if
you think about it it'll also interfere
with the absorption of a whole host of
medications so patients on kaopectate be
aware that your other medications are
probably being bound it's really
important I'm just going to stop here
and I'm going to say do not use anti
diarrheal agents in patients who have
bloody diarrhea or infectious diarrhea
because the diarrhea in those cases are
actually cathartic in the truest sense
of the word meaning that you're getting
rid of the infectious agent and diarrhea
in this case is a protective mechanism
from the disease so if you inhibit the
protective mechanism you make the person
much sicker we're going to cover this in
more detail in your GI systems lecture
by lecture you later
but I just want to put that out there
now
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