Renin Angiotensin Aldosterone – Drugs in Hypertension

00:01 Okay. Let's move on to RAAS agents, the renin angiotensin aldosterone pathway.

00:08 So, let's take a look at how the pathway works.

00:11 We start off with the prohormone called angiotensinogen.

00:16 In the kidney, renin converts angiotensinogen into angiotensin I.

00:23 And it is then converted by the angiotensin converting enzyme into angiotensin II.

00:29 Now, ACE inhibitors will block this particular enzyme.

00:33 And when that happens, you will have less angiotensin II.

00:41 Now, the other thing that happens with this agent is that when you block the conversion of angiotensin I into angiotensin II, you're also similarly blocking the breakdown of bradykinins.

00:53 Now, bradykinins are things that you don't really want in the body because they can cause cough and these other symptoms that I've got listed here.

01:01 So, ACE inhibitors cause cough because they also inhibit the breakdown of bradykinin.

01:08 Let's get back to angiotensin II.

01:11 You notice on the end of our slide there, on the far end of our slide, we also have non-ACE pathways.

01:17 So there is still some conversion of angiotensin I into angiotensin II even if you blocked the ACE enzyme with an ACE inhibitor.

01:26 This brings us down to the angiotensin receptor.

01:29 So, we have angiotensin receptor blockers.

01:33 And what we want to do is we want to block the production of aldosterone.

01:38 Now remember that aldosterone has lots of effects on the body.

01:42 It decreases water and sodium excretion, and it will actually cause a higher blood pressure.

01:48 So, by giving a drug that blocks the conversion of angiotensin II into into the various aldosterone molecules, it's going to be very important so that's why we block it with the ARB.

02:01 Now remember, I already mentioned that spironolactone is an aldosterone blocker, it blocks it right at the receptor site so it's a very effective agent as well.

02:10 But the downside is, is that for using an ACE inhibitor or an ARB, we're not going to be using spironolactone for the specific reason that we don't want the potassium to go too high.

02:24 The new direct renin inhibitors.

02:27 There's only one drug in this drug class called aliskiren, acts directly at the level of renin to prevent this whole cascade from occuring.

02:37 Now, let's go over the different groups of drugs in this class.

02:42 So, the ACE inhibitors are listed here.

02:44 This is actually, believe it or not, only a partial list, but these are the most commonly used drugs.

02:50 The prototypical drug is captopril, the one I also want you to remember is enalapril.

02:55 And quite frankly, in clinical practice I use neither now, but for the purposes of exams, those are the ones that you want to remember.

03:03 ACE inhibitors, if you noticed, end in P-R-I-L, -pril.

03:07 So, anything that's a -pril, is generally an ACE inhibitor.

03:12 The angiotensin receptor blockers end in -sartan.

03:16 So, there's candesartan, eprosartan, irbesartan.

03:19 The prototypical drug is actually losartan, but if you remember any of them, you'll be fine.

03:24 The direct renin inhibitors or renin inhibitors is aliskiren.

03:28 It's sold as Rasilez in well pretty much everywhere in the world.

03:32 It's a sole drug, it is going to be important to know for your exam and we'll talk about its clinical use in a minute.

03:41 And then finally, the aldosterone antagonists like spironolactone, they fall into two categories.

03:47 I mentioned them already in the diuretic section of our lecture, but I also mention it here because it is technically a RAAS drug as well.

03:55 Let's compare the two major groups of renin angiotensin aldosterone drugs.

04:02 Let's compare ACE inhibitors head to head to the ARBs.

04:05 First of all, let's just say that both classes of drugs are really fantastic antihypertensive agents.

04:11 And in my books, I think they are the first class of drugs that you would want to choose.

04:15 In guidelines, whether they are the British guidelines, the Canadian guidelines or the American guidelines, we talk about having several classes as first line agents.

04:26 But in practicality, most people go to one of these two agents first.

04:31 In many many studies, they have been shown to be beneficial, both in morbidity and mortality.

04:37 That includes heart failure, microvascular disease which includes retinopathy and nephropathy, as well as left ventricular hypertrophy reduction, and even stroke reduction through it's blood pressure actions.

04:51 So, let's talk about the side effects from these medications.

04:55 Hyperkalemia is a common side effect with ACE inhibitors, about 1 in 100 patients will develop it.

05:01 It's slightly less with the angiotensin receptor blockers at 0.3 %.

05:06 A cough is quite common in ACE inhibitor patients.

05:11 The studies will tell you it's anywhere between 2 and 20%.

05:14 I personally believe that that's underestimating the numbers.

05:18 The ARBs will tell you that the cough rates are around 0.001 %.

05:24 I personally have never seen a credible case of cough brought about by ARBs.

05:28 So the ARBs are clearly superior in terms of cough, and in many cases when a patient comes in complaining of cough on an ACE, we put him on an ARB.

05:37 Pancreatitis, depending on what region of the world you're in, the rates are about 1 in 5,000, so guaranteed you will see one in your practice.

05:47 The pancreatitis rates with ARBs is about 1 in 15,000.

05:53 Now, if you have a patient who's on an ACE inhibitor, and they develop pancreatitis, should you put them on an ARB? The answer is no, because now, that ARB patient has a 1 in 10 risk of developing pancreatitis.

06:07 And that's just simply too high.

06:09 At that point, I would use a different type of blood pressure drug.

06:14 Angioedema is another potential risk factor with both drugs.

06:18 Angioedema's risk factor are around 1 in 2,000 with the ACE inhibitors, depending on what study you're looking at.

06:24 And with the ARBs, we get numbers roughly around 10 times less or 1 in 20,000.

06:30 Once again, if you develop angioedema on an ACE inhibitor, I generally don't recommend that you use an ARB, try using a different class of drug.

06:40 Going on to the aldosterone antagonists and the direct renin inhibitors, the aldosterone antagonists are poor antihypertensive agents, but we still use it quite a bit as a fourth line drug.

06:53 The direct renin inhibitors are actually very good antihypertensives, and in particular, they are good in a special kind of hypertension called hyperreninemic hypertension.

07:05 In large scale studies, we've actually shown mortality reduction and morbidity reduction, especially in heart failure.

07:12 The direct renin inhibitors have small scale studies and pilot studies showing improvement in heart failure or projected improvements in heart failure.

07:22 In terms of side effects, hyperkalemia is rare.

07:27 Side effects of diarrhea are often seen with the direct renin inhibitors.

07:33 Remember that you do get feminizing characteristics because it has an antiandrogen activity.

07:38 This is actually used as an advantage in many women who have hirsutism, and one of the side effects with the direct renin inhibitors is potential headache, although that potential risk is kind of small.

07:51 Let's move on to principles of therapy using RAAS drugs.

07:57 We do not combine ACE inhibitors and ARBs.

08:01 ACEis and ARBs are often combined with a diuretic.

08:05 And we prefer hydrochlorothiazide as our agent of choice because hydrochlorothiazide causes a low potassium and ACEis and ARBs causes high potassium and they seem to balance out.

08:18 ACEi's and ARBs are often combined with a calcium channel blocker as well.

08:22 They are particularly potent in this combination and in fact, in the United States, and in other regions of the world, you can purchase pills that have an ACE inhibitor and a calcium channel blocker, or an ARB and a calcium channel blocker, all in one tablet.

08:39 ARBs are much better tolerated in most patient populations.

08:43 And quite frankly, they're more likely to be taken long term by your patients.

08:48 A major study done in Canada showed that ARB compliance at two years was about 80%, whereas ACE inhibitor compliance was about 40% in the same patient population at the same time.

09:01 So, ARBs tend to be taken by the patients, on a more regular basis, for a longer time.