Let’s finally talk about a third class of
drugs - diuretics. Because particularly in
the heart failure state, you want to encourage
the loss of sodium and the loss of water,
as we talked about with the ACE inhibitors
and the angiotensin receptor blockers. But,
sometimes, those two agents are not enough,
you don’t get rid of enough fluid. So, what
do you do? You give at the same time, a diuretic.
What the diuretic does is it paralyzes, in
part, the kidney’s ability to resorb, to
recapture salt and water. So, what happens
is you produce more urine, in which there’s
lots of salt and water, and you get rid of
the excess water that’s been retained. For
example, the slide I showed you in the physical
exam where there was a lot of edema, where
you could push your finger into the soft tissues
and leave a mark. Obviously, there was much
too much salt and water being held on to in
that patient. That would be somebody that
we.. if the heart was decreased functioning,
we would be giving a beta blocker, we might
be giving an angiotensin-converting enzyme
inhibitor or an angiotensin receptor blocker
and we would be giving a diuretic.
I am just going to talk about one diuretic.
What you see in this diagram is that we have
three classes of diuretics, some more powerful
than the others. And by the way, each of these
also lower blood pressure, so they are often
used in hypertensive patients as well. So,
there’s a double use for the diuretics.
In the heart failure state, they help you
to get rid of salt and water and in hypertension,
they help to control the blood pressure. So,
the commonest form of diuretics that are used
are the thiazide diuretics. These are moderate
in strength and they are very commonly used.
They are also generic, so they are inexpensive.
Again, they are one of the commonest treatments
initially for hypertension - for high blood
pressure. But, they also can be used in mild
heart failure states. In more advanced heart
failure states, we use something called “loop
diuretics.” Furosemide is one of those.
That’s a much more powerful diuretic. It
induces a much stronger release of urine,
but also runs the risk of dehydrating the
patient. So again, you know, you have got
to balance these things. It’s like making
fine food, you don’t just dump the spices
in in huge amounts. You put a little in, you
taste it. The same thing happens in the clinical
situation. You put some in, you monitor the
effect. Is it enough? If it’s too much,
you back off. If it’s not enough, you advance
a little bit.
The thiazide diuretics; Here’s a list of
them. The commonest ones are chlorthalidone
and so-called “HCTZ,” which stands for
“hydrochlorothiazide.” We often write
it in the simple abbreviation because that’s
a real mouthful - hydrochlorothiazide.
And I most commonly use HCTZ, but many doctors
like chlorthalidone. They both lower blood
pressure and they both cause a diuresis that
is a loss of sodium and water. In fact, chlorthalidone
is more powerful. You can see in this slide
taken from a research study that compared
the blood pressure lowering effect of chlorthalidone
to that of hydrochlorothiazide and you can
see the… the effect was stronger with chlorthalidone.
But, unfortunately, the side effects were
also worse with chlorthalidone. It caused
more loss of sodium and water and one of the
side effects from these diuretics, from all
diuretics in fact, is loss of potassium in
the urine. If you lower the potassium in your
body, you can have muscle cramps, you can
have a tendency towards cardiac arrhythmias.
And so, lowering potassium is not a good idea.
We often give patients supplemental potassium
when we give diuretics. But, in the case of
chlorthalidone, hypokalemia or a drop in blood
potassium level with its complications, is
more common with chlorthalidone. So, you see
sort of the yin and the yang here. Hydrochlorothiazide
- less powerful at lowering blood pressure,
but less likely to cause low potassium, hypokalemia.
Chlorthalidone - better at lowering blood
pressure, a little more powerful diuretic,
but more likely to cause hypokalemia. So,
you have to think about the patient, think
about the situation you are using it in when
you decide for one or the other. Another one
of the side effects from thiazide diuretics is
that they increase the likelihood of a gouty
arthritic attack with deposit of uric acid
in the joint capsules that causes an inflammation,
a... a very painful form of arthritis. That’s
not too common, but in certain individuals
who are predisposed, it can make it worse.
And of course, you can also dehydrate the
patient with the diuretics, lowering the blood
pressure and even increase the likelihood
of the patient fainting. Particularly in a
warm and dry environment, such as that that
I live in in Arizona, there’s a great tendency
towards dehydration. So, you have to be very
careful when you use diuretics, particularly
in the summertime when it’s very hot and
So, in conclusion then, we have talked about
three classes of drugs that are exceedingly
commonly used. They are almost all of them
generic, they are all of them reasonably
priced and they are all of them very effective.
But, you have to use them carefully because
of the potential for side effects. You have
to consider each patient as an individual
that requires careful thought before you prescribe
one or another of these drugs.
In the next lecture, we are going to continue
to talk about other cardiovascular drugs and
their uses. Thank you for being with me today.