Okay, we're going to do chapter six cardio
diuretics and we're going to compare
four different classes of diuretics starting with the osmotic diuretic mannitol, brand Osmitrol,
loop diuretic furosemide, brand Lasix,
thiazide diuretic hydrochlorothiazide, one of the brand names is Hyrodiuril, there's a couple but usually you'll just see this as generic,
and then potassium sparing diuretic spironolactone, brand Aldactone.
There is a triamterine which you'll see a lot with hydrochlorothiazide,
but just for simplicity's sake we're going to just stick with one.
Again, the way you want to remember these is to go through the nephron from the glomerulus down the s-curve
from the proximal convoluted tubule then to the ascending loop of henle then to the distal convoluted tubules.
So the osmotic diuretic - and I can get my little pointer here -
so the osmotic diuretic is going to be closest to the glomerulus. This is going to be used for some kind of intracranial
hemorrhage kind of things like that.
Loop diuretics, you'll probably see with more severe conditions, edemetous conditions like
congestive heart failure.
Thiazides are usually going to be a first choice when you're talking about blood pressure, hypertension, things like that.
Potassium sparing diuretic generally are going to be paired with a thiazide diuretic or something like that to prevent the hypokalemia.
Okay, so let's turn off the laser pointer, right?
So practice question - 'A diuretic that works in the proximal convoluted tubule and reduces intracranial pressure?'
Again, we're going to use all of these four drugs over again But we'll go through it a little bit more slowly this first time
A) osmotic diuretic - mannitol (Osmitrol)
B) loop diuretic - furosemide (Lasix)
C) thiazide diuretic - hydrochlorothiazide (Hydrodiuril)
D) potassium sparing diuretic - spironolactone (Aldactone)
Again, remembering that we're going from the glomerulus to the proximal convoluted
tubule, the ascending loop of henle, the distal convoluted tubules, and then the collecting duct.
In this case,
we're talking about mannitol, which works in the PCT, and it reduces intracranial pressure,
something that we'd use really only in an emergency something like that, okay?
Let's think what would happen if we're talking about the loop of Henle, so
if we have something working in the loop of Henle, and
might have some kind of a side effect,
we'd be talking about furosemide, so this makes B correct.
The loop of Henle, when we talk about the ascending loop of Henle,
we can go into the details with the exchange, but just know that because
it's closer to the glomerulus,
we're really going to see more diuresis,
so someone that has a more severe condition like CHF would probably be on furosemide versus somebody that has a less severe condition like
hypertension,
and that works in the loop of Henle.
Ototoxicity,
loop diuretics are infamous for this. We always want to be careful watching for gentamicin or other drugs that have
ototoxicity as a side effect.
'Which medication cannot be used in renal failure and is the first-line medication in hypertension?'
Hydrochlorothiazide - we can
use it as a thiazide diuretic, it makes sense in hypertension - but why doesn't it make sense in renal failure?
Well, when you're talking about renal output and
how these diuretics work, if you're going to have somebody with renal failure,
hydrochlorothiazide is just not going to be effective.
You're going to have to use something like a loop diuretic because of a different mechanism of action.
Okay, and then the last one - so what can cause hyperkalemia
and acts on the renin-angiotensin-aldosterone system?
The hyperkalemia, again we're talking about the collecting duct where we're probably exchanging something like sodium for potassium, and
we're actually getting it back. Spironolactone,
if you want to think about what it does, it's an aldosterone
antagonist. Again, aldosterone is meant to help us increase blood pressure by holding on to sodium and water,
but in holding on to sodium and water it releases potassium.
If we would reverse that with the medication, we're going to release sodium and water and then we retain potassium.
That's why we end up with this hyperkalemia and acting on the renin-angiotensin-aldosterone system.
Knowing the physiology again, what aldosterone does - holding on to sodium,
the water following the sodium and then exchanging for potassium is how we end up with a potassium
sparing diuretic or a diuretic that
creates an increased potassium.