Diuretics – Cardiovascular Pharmacology

00:01 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.

00:25 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.

01:11 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.

01:26 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.

01:43 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.

03:15 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.

03:38 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.

04:41 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 very dry.

05:00 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.

05:25 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.