Alpha Agonists – Drugs in Hypertension

by Pravin Shukle, MD

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    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.

    About the Lecture

    The lecture Alpha Agonists – Drugs in Hypertension by Pravin Shukle, MD is from the course Cardiovascular Pharmacology. It contains the following chapters:

    • α-Agonists
    • α-Methyldopa and Clonidine

    Included Quiz Questions

    1. Methyldopa
    2. Clonidine
    3. Angiotensin-converting enzyme inhibitors
    4. Hydrochlorothiazide
    5. Diuretics

    Author of lecture Alpha Agonists – Drugs in Hypertension

     Pravin Shukle, MD

    Pravin Shukle, MD

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    By Robert R. on 03. April 2020 for Alpha Agonists – Drugs in Hypertension

    Very pleasant pace of lecture and clear explanation. Also love the quick and personal response on the questions on the forum. Really makes me feel like I am in the lecture hall itself.