Alpha Agonists – Drugs in Hypertension

00:01 Let's move on to those drugs that act on the sympathetic nervous system, specifically we are just going to focus on alpha agonists right now.

00:10 So, these alpha agonists are often very good drugs. There we have the alpha 1 agonists like phenylepherine, and alpha 2 agonists like alpha-methyldopa and clonidine.

00:22 Now, phenylepherine is an alpha 1 agonist and that will actually cause constriction of the blood vessel and it causes high blood pressure. So, we put it there just to remind you that alpha 1 and alpha 2 have very different effects. Obviously, we don't use phenylepherine to treat hypertension because it causes high blood pressure.

00:42 Let's go on to the alpha 2 agonists. So, alpha-methyldopa and clonidine.

00:49 Let's compare and contrast alpha-methyldopa and clonidine.

00:53 The alpha-methyldopa or I'm going to call it Aldomet for simplicity sake, decreases central sympathetic outflow.

01:00 Similarly, clonidine does the same thing.

01:04 Aldomet is a prodrug. It is metabolized to the active agent.

01:11 Both will decrease central sympathetic outflow, cardiac output, and vascular resistance.

01:20 Both have a compensatory reaction of salt retention. They both do this.

01:27 There are some idiosyncratic reactions which distinguish the two drugs.

01:31 The idiosyncratic reaction of note with Aldomet is hemolytic anemia.

01:36 The idiosyncratic reaction of clonidine is rebound hypertension.

01:42 Both of course cause sedation cause they're working centrally.

01:47 In terms of use, Aldomet was previously used extensively in pregnant patients.

01:52 In fact, Aldomet is the second most common antihypertensive drug used in pregnant women, whereas clonidine is definitively categorically not used in pregnancy.

02:04 So, these two drugs are very very different in one very important respect, is that Aldomet is used in pregnancy, clonidine is never used in pregnancy.