Welcome to Pharmacology
I'm Dr. Pravin Shukle.
We're going to be covering
GI pharmacology today.
The drugs used for gastrointestinal
order spend a huge range of medications.
We have drugs for peptic acid
disease, drugs for pro-motility,
drugs for irritable
drugs for inflammatory bowel
disease, and anti-emetics.
We have a whole host of other
agents as well for various ailments.
Let's look at
peptic acid disease.
We have the antacids,
the H2 blockers, the PPIs,
the mucosal protective
agents, and the antibiotics.
Let's start off
with the antacids.
Now, antacids are weak
bases that neutralize
the low pH environment
of the stomach.
These can include many agents
such as magnesium hydroxide
which is better known
as Milk of Magnesia.
Milk of Magnesia is a
mainstay of antacid therapy
and it's probably the first line
agent that we use in most cases.
It has a strong laxative effects
so it's very good for patients
who are also constipated.
Another agent that we use
is aluminum hydroxide,
commonly known as Maalox.
It has a strong constipating effects so
it's better for people who have diarrhoea.
And calcium carbonate and sodium
bicarbonate are just plain antacids.
They are absorbed by the
gut unlike the other agents.
The first two agents that I
mentioned tend to stay in the gut,
these agents are
actually get absorbed.
Let's move on to the H2
These agents block histamine at the
H2 receptor inside the gastric mucosa,
specifically the parietal cells.
You can see that they inhibit
stomach acid production directly,
especially at night, so this is a
particularly good agent for people
who have night
time GERD symptoms.
They are relatively
they are actually sold
over the counter now.
Cimetidine was the original and
prototypical drug in this drug class.
But we actually don't use it because
there are multitude of drug interactions
that we get from this
Interestingly enough, some of these
agents, in particular cimetidine,
do have an antiandrogen
effect as well at high doses.
These are the agents
that are commonly sold.
These agents are sold
over the counter.
They're extensively used
all around the world.
Let's move on to the PPIs or
the proton pump inhibitors.
These are lipophilic weak bases.
So the agents themselves
are not antacids.
What they do is they
and they work inside
the parietal cells
and they get concentrated in
these areas up to 1,000 times.
They irreversibly inactivate the
What this does is that it ends up causing
less acid secretion, substantially less.
Now they are
They may take 3 to 4 days to actually
have an effect because of this reason.
They are far more effective than the H2
antagonists that I spoke about earlier
but they last, and they work well, and they
are the mainstay of anti-ulcer therapy.
There are some toxicity issues
associated with the PPIs.
You can get diarrhoea,
abdominal pain and headache.
And you can get hypergastrinemia
if you use them for a long time.
They may also decrease
the ability of drugs
that require higher acid levels.
So for example, ketoconazole
requires a high acid environment
within the stomach to become
particularly activated and absorbed,
if you give a PPI the same
time as you give ketoconazole,
you're going to reduce the availability
of ketoconazole to the body
for it to do its job.
The same thing will happen
with drugs like digoxin.
Now, a small increase in
respiratory and enteric infections
are associated with PPI use.
We have many brands out
on the market today,
prototypical drug is omeprazole,
but you have a whole list of other
ones that I've given you here.
Let's move on to the
mucosal protective agents.
Now the prototypical example
of this is sucralfate.
It's a very poorly
inside the stomach.
And when I say polymerize what I mean
is is that it forms chains of molecules.
This polymer will bind to the injured
tissue inside the patient stomach.
And it forms a protective
coating over those ulcers
and prevents further
damage from occuring.
The down side of this medication is
it has to be taken 4 times a day.
And that's really the main reason why
we don't use it as much as we used to,
simply because of
It's a very low toxicity agent.
It has a very low solubility.
It's quite effective,
unfortunately it's inconvenient.
These medications are
great for patients
who are very adherent
to their schedule
and so if you know these patients are
going to follow their instructions,
it's a great choice.
Let's move on to other agents.
Misoprostol is an analogue
of prostaglandin E.
It works at almost the same
point in the system as the PPIs.
You get increased
because it directly
inhibits acid secretion.
And it reduces ulcers
in NSAID users as well.
The adverse event rate is quite
high because it's poorly tolerated.
There's lots of GI upset and
diarrhoea associated with this agent.
And for this particular reason,
it's not used much anymore.
It is an agent however
that you should be aware of
because it is going to be on
pharmacology portion of your exam.
Let's move on to agents
like colloidal bismuth.
So, bismuth subsalicylate,
also called Pepto-Bismol,
gives a protecting coating on
ulcerated tissue much like sucralfate.
It stimulates mucosal
protective systems as well,
so it goes a little bit further
than sucralfate in that sense.
It actually has direct
And you actually have some
sequestration of enterotoxins.
So if there are
toxins within the gut,
it actually binds those toxins and
rendor them biologically unavailable.
It reduces stool frequency
in infectious diarrhoea.
And unfortunately, there is a cosmetic
side effect of this medication,
it causes a black tongue.
Now the other important issue that you have
to remember is it also causes black stools.
And many times, people who have
melena type stools from Pepto-Bismol
are misdiagnosed as
having GI bleeds.
That is not the case.
So be aware that if you have a patient
who presents with melena type stools
ask first if they were
taking this agent.