Sympathetic Blockers

by Pravin Shukle, MD

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    Let's talk about sympathetic blockers in the eye. The sympathetic blockers are used to block that fight or flight reflex. So remember sympathetic system wants to open up the iris. So blocking that ability to see in the dark blocks the dilation of the iris. And blocking the creation of intraocular pressure because it blocks the secretion of the aqueous humor or the liquid inside the eye. So timolol and levobunolol are eye drops that are used for glaucoma. It decreases the secretion of aqueous humor and the side effect is pinpoint pupil or miosis. Partial agonist activity is kind of a unique concept where the beta 1 blockers act as a blocker but those same drugs have a little bit of agonist activity on the beta 2 receptor. So this is good for the asthmatic patient. An example of that is acebutolol and labetolol. So remember that you have one heart and two lungs, right. So beta 1 is for the heart, beta 2 is for the lung because you have two lungs. So if you block the effects of adrenaline on the heart, you slow down heart rate. If you block the effect of adrenaline on the lungs which are designed to normally breathe when you are under stimulation. If you block the beta receptors in the lung, you actually stimulate asthma. But if you are a agonist for beta 2, you will treat asthma, you will help the asthma get better so you can breathe better. That's why acebutolol and labetolol are theoretically better in asthmatic patients. I just want to mention very quickly another beta blocker called nebivolol. This newest beta blocker has also activity on nitric oxide. So this drug is now available in the United States, recently available in Canada. It's been in Europe...

    About the Lecture

    The lecture Sympathetic Blockers by Pravin Shukle, MD is from the course ANS - Pharmacology.

    Included Quiz Questions

    1. Hypertension
    2. Exacerbation of asthma symptoms
    3. Masked symptoms of hypoglycemia
    4. Sexual dysfunction
    5. Excessive bradycardia
    1. Nebivolol
    2. Acebutolol
    3. Propanolol
    4. Levobunolol
    5. Labetolol
    1. They have partial agonist activity on beta 2 receptors in the lungs.
    2. They have agonist activity on b1 receptors in the lungs.
    3. No beta blockers should be used on patients with asthma.
    4. They are unable to reach the lungs due to pharmacodynamics.
    5. They are selective for b1 receptors over b2 receptors.

    Author of lecture Sympathetic Blockers

     Pravin Shukle, MD

    Pravin Shukle, MD

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