Pharmacology – ALPHA & BETA BLOCKERS – ADRENERGIC ANTAGONISTS ( MADE EASY)

Pharmacology – ALPHA & BETA BLOCKERS – ADRENERGIC ANTAGONISTS ( MADE EASY)


in this lecture I’m going to talk about
adrenergic antagonists so let’s get right into it
adrenergic antagonists also called sympatholytics bind to adrenergic receptors but instead of stimulating them they actually prevent their
activation and just like with adrenergic agonists we can divide antagonists based
on their affinity for alpha or beta receptors so we can divide adrenergic
antagonists into two main groups that is alpha blockers and beta blockers so
let’s start with alpha blockers first alpha-1 adrenergic antagonists block
the binding of norepinephrine to the smooth muscle receptors which results in
vasodilation and thus lowering of blood pressure this is why alpha blockers are
useful in the treatment of hypertension now alpha blockers can be subdivided
into two groups that is non-selective alpha blockers and selective alpha
blockers as you might have guessed non-selective agents can block both alpha-1
and alpha-2 receptors example of these are Phentolamine and Phenoxybenzamine which are used in the treatment of hypertension specifically caused by
pheochromocytoma which is a tumor of the adrenal glands that secrete
norepinephrine and epinephrine now we know that through alpha-1 blockade these
drugs cause vasodilation but since they are non-selective they also block alpha-2 receptors which as you may remember from the previous lecture are mainly
located on presynaptic nerve endings now norepinephrine acts on alpha-2
receptors to inhibit its own release so blockade of these receptors results in
more norepinephrine release norepinephrine then can stimulate beta-1
receptors on the heart this is why non-selective drugs such as Phentolamine and Phenoxybenzamine can cause tachycardia and even cardiac arrhythmias
now the main difference between these two
drugs is that Phenoxybenzamine is a irreversible antagonist and the only way
the body can overcome its effects is by making new adrenergic receptors which
takes about 24 hours or so on the other hand Phentolamine is a reversible
antagonist and that’s why its effect lasts only about four hours or so now
let’s move on to selective alpha blockers and let’s discuss alpha-1
blockers first so these agents selectively and reversibly block alpha-1 receptors located mainly in vascular smooth muscle which reduces peripheral
resistance and leads to decrease in blood pressure and they also block
receptors in the smooth muscle of the bladder neck and prostate gland which
causes smooth muscle there to relax leading to relief of the urinary
difficulties associated with benign prostatic hypertrophy BPH for short or
simply enlarged prostate now examples of alpha-1 selective
blockers include Prazosin Doxazosin Terazosin Tamsulosin Alfuzosin and Silodosin and note that this ending with “-osin” is a pretty good
giveaway when it comes to identifying alpha-1 blocker now the first three of
these that is Prazosin Doxazosin and Terazosin are effective treatment
for hypertension but have lesser effects on relieving symptoms of enlarged
prostate on the other hand Tamsulosin Alfuzosin and Silodosin have little
effect on blood pressure but are much more effective for relieving symptoms
associated with enlarged prostate and this is because these agents have
increased selectivity for alpha-1 receptors in the prostate specifically
alpha-1a subtype now when it comes to side effects orthostatic hypotension is
one of the main concerns when initiating alpha-1 blocker
although it’s not as severe as that observed with non-selective alpha
blockers additionally vasodilation produced by alpha-1 blockers can lead
to headaches and nasal congestion finally what about alpha-2 selective
blockers well alpha-2 selective blockers have very limited clinical
application in humans and they’re used mainly in research one example of alpha-2 blocker that you may encounter is Yohimbine which can be found in some
dietary supplements however there is not much beneficial evidence supporting its
use in humans on the other hand Yohimbine is used sometimes in veterinary medicine to reverse sedative effects of alpha-2 agonist such as Xylazine now
let’s switch gears and let’s move on to beta blockers so just like alpha
blockers beta blockers can also be subdivided into selective and
non-selective agents however unlike alpha blockers beta blockers can also be
grouped in generations beta blockers are competitive inhibitors at beta
adrenergic receptors and they counter the effects of catecholamines such as
epinephrine and norepinephrine which leads to decrease in sympathetic effects
mainly on cardiovascular system this is why beta blockers are useful in the
treatment of hypertension heart failure heart attacks angina and cardiac
arrhythmias additional uses include treatment of glaucoma and migraine
prophylaxis so now let’s start by discussing first generation beta
blockers which also happen to be non-selective that is they block beta-1 and
beta-2 receptors throughout the body example of these agents include
Propranolol Pindolol or Nadolol Sotalol and Timolol now practically all
the applications of these agents are based on blockade of beta-1 receptors on
the heart which results in decreased heart rate delayed conduction through AV
node and reduced contractility so now the final outcome is decreased cardiac
output and decreased oxygen demand of heart muscle besides being useful in
treatment of hypertension angina and arrhythmia
note that Propranolol due to its lipophilicity can also penetrate into the CNS
and was found to be effective for migraine prophylaxis on the other hand Timolol when applied topically to the eye was found to decrease intraocular
pressure which is why it is often used for a treatment of glaucoma
however all that being said let’s not forget about blockade of beta-2 receptors by
these non-selective agents and as you may recall beta-2 receptors are predominant
in lungs so their blockade can actually lead to bronchoconstriction for this
reason these non-selective beta blockers are not recommended in patients with
COPD or asthma now let’s move on to the second generation beta blockers which
happen to be selective for beta-1 receptors and because of that we also
call them cardio-selective beta blockers now this cardio-selectivity makes these
agents more suitable in patients with chronic lung disease however keep in
mind that at high enough doses this beta-1 selectivity can be lost and beta-2
receptor blockade may occur example of these agents include Atenolol Acebutolol
Bisoprolol Esmolol and Metoprolol now let’s move on to the third generation
beta blockers and here you need to pay special attention because things can get
a little tricky so unlike the first generation group that included non-selective agents and unlike the second generation group that included selective
agents the third generation group includes both non-selective and
selective beta blockers however what makes the third generation beta blockers
different from the other two is that they also act on blood vessels to cause
vasodilation so here we have non-selective agents
such as Carvedilol and Labetalol which produce peripheral vasodilation by
blocking not only beta but also alpha-1 receptors and on the other hand we
have beta-1 selective agents such as Nebivolol which produce vasodilation by
inducing the release of nitric oxide from endothelial cells and Betaxolol
which is thought to produce vasodilation by additionally blocking calcium
channels and just as a side note here Betaxolol due to its ability to
decrease intraocular pressure when applied topically to the eye just like
Timolol it is often prescribed for glaucoma but the bottom line here is
that vasodilation produced by the third generation beta blockers make
these agents especially effective in treatment of hypertension furthermore
Carvedilol and Nebivolol have been also shown to have antioxidant properties
which make them beta blockers of choice for heart failure alongside commonly
prescribed Bisoprolol and Metoprolol lastly I wanted to briefly discuss intrinsic
sympathomimetic activity of couple beta blockers namely Pindolol and Acebutolol now these two beta blockers are a little special in that they have ability
to not only block but also to weakly stimulate both beta-1 and beta-2
receptors which leads to diminished effect on cardiac rate and cardiac output this
so called intrinsic sympathomimetic activity can actually be beneficial in
patients who cannot tolerate other beta blockers because of pre-existing
bradycardia or heart block and now before we end you may wonder well what
about beta-2 blockers and the short answer is at this time we don’t have
clinically useful beta-2 blockers and with that I wanted to thank you for
watching I hope you enjoyed it and as always stay tuned for more videos

100 Comments

  1. it was really good and benificial sir plzzz tell me how to memorize the drugs name?? as my papers are on peek i have to work hard and im confused between all ANS Drugs

  2. Umm Clonidine and Methydopa are alpha 2 blockers used to treat ADHD and Hypertension…You may want to update that.

  3. I want to ask something:
    1.In previous video norephineprin mainly stimulate alpha 1 receptor which increase blood pressure and almost dont stimulate beta receptor. But here, norephineprin stimulate beta 1 receptor and not alpha 1 receptor?
    2. In nonselective alpha blocker, alpha 1 & alpha 2 blocked. Alpha 2 blocker causes norephineprin release more, but why it doesnt have an effect to alpha 1 receptor that cause increase blood pressure. And moreover nonselective alpha blocker used for hipertention that needs low blood pressure.
    I still get confused abt this, please answer me, thank you..

  4. waaaoooh ! waaooooh ! thank you ! it's genious …we need your vidéos and we hope that it will be in french ! pleeeeeeaaase I'm in love with your vidéos ! so please … make them with french
    for the sake of God

  5. I have been reading for two hours about alpha blockers but there were many things I didn't understand. In here only five minutes but It did answer all my questions. Amazing ,Thanks 😄

  6. THANK YOU!!! I loved this video, its simple, clear to understand and I love the graphics that go with it. Will be watching your other videos. 🙂

  7. I already subscribe coz I’m in my mid to late 60s w HBP for the past 15 plus yrs, it’s so easy to understand & learn what alpha & beta blockers are & how they function in treating HBP & for those w heart prob, something doctors don’t do or explain b4 they write a prescription, how can a patient know & understand what & how this med that was just prescribe, I guess all we have to do is get & take, which is & have been the norm unless we ask questions, so these videos are so informative & teach us what they’re suppose to do, ThankU so much for ur kindness & good hearted work the time & effort, may God bless you & yours, w good health & happiness, especially in 2018 & beyond, keep up the good work, ThankU & Happy 2018!!

  8. For the first time l have subscribe a channel on YouTube!
    your channel is really useful.
    I want to ask you, if i want to study pharmacology from a textbook, can you suggest one for me?
    Thank you.

  9. Helo… You said alpha blockers used to dilates… Well all I know that this is not true… Beta blockers are responsible for dilation

  10. Wow thanks for this video, good summary with pictures!! Had to subscribe, I needed this since I have an exam and this puts it all together. Thanks again.

  11. Very good and fruitful short lecture!
    If we read the Lippincott Pharmacology book along with these lectures, it will be very high efficient for us.

  12. Guys, here is a way to remember which drugs belong to what group between the 1st generation and 2nd generation drugs of the BETA Blockers. (Note: this method only works for the drugs mentioned in this video). So just remember the letter M, which is the letter that comes in the middle of the alphabet (there are 26 letters in the alphabet, it is the 13th letter). So any drug that starts with any letter from A through M (so any drug that begins with a letter in the first half of the alphabet) belongs in B1 selective antagonists and any letter that starts from N through Z (so any letter that starts with a letter in the second half of the alphabet) belongs in non-selective (1st generation) BETA blockers. Hope this helps…

  13. Tysm fr the video…… It is very useful n easy to learn as well…….. After watching this video once if v go through the text book it becomes easy to understand… Tysm 😍

  14. I had ed due to over use of pains enlargement device as pump. I had symptoms called in Internet hard flaccid. Which my cc contract. I go many doctors who help nothing they said psychological ed. I read hard flaccid hf is sns reaction which made my penile smooth muscle did not relax to full capacity. Can alpha blocker help me?
    Because I had this chronic problem for 8 years
    Please help me doctor….

  15. Edit Dec 24, 2018 .. Edit these later.
    1:25 Phentolamine, phenoxybenzamine for hypertension caused by Pheochromocytoma (tumor that secretes norepinephrine, epinephrine. Acts on A2 receptors to inhibit its own release so blockade of these receptors result in more no-rep release. Norep stimulates –> B1 receptors on heart … that's why non-select P,P can cause Tachycardia and cardiac arrhythmia.
    Phenoxybenzamine is an irreversible antagonist and only way body can overcome it is if body makes new adrenergic receptors which takes about 24 h.
    Phentolamine is reversible antagonist (lasts 4h
    2:50 Selective block A1 receptors located mainly in vascular smooth muscle which reduces peripheral resistance and leads to decreased BP and also relaxes smooth muscles in the bladder neck –> USED for BPH (enlarged Prostate)
    3:28 Think "zoesin"
    3:40 Prazosin PDT
    Doxazosin hypertentsioin ( little effect on BPH
    Terrazosin
    Tamsulosin
    Alfuzosin BPH (little effect on BP) because these targets A1 in prostate
    Silodosin
    4:30 Vasodilation
    5:18 A & B are both has selective and non-selective
    5:30 Beta blockers are competitive inhibitors at beta adrenergic receptors and they counter effects of catecholamines (Epinephrine, Nor Ep) ( which is why this is useful in treatment of hypertension, HF, H attack, angina, cardiac arrhthmias, also treatment of glaucoma and migraine prophylaxis
    6:20 1st gen PIC. Propranolol, Pindolol, Nadolol, Sotalol, Timolol.
    acts on B1 receptors on heart –> HR down , delayed conduction through AV node and Contractility down so the final outcome is less Cardiac otuput and decreased oxygen demand on the heart muscle
    6:49 Propranolol can penetrate to CNS ,, can be used for migraine prophylaxis
    7:00 Timolol eye = reduces intraocular pressure
    7:17 B2 receptors in lungs (*these being blocked –> bronnchoconstriction (DON'T if COPD, asthma
    7:38 B blocker 2nd generation (targets B1 receptors) / cardioselective beta blockers
    BEAMS atenolol , acebutolol , Bisoprolol , Esmolol , Metoprolol
    8:20 3rd generation has selective and nonselective B blockers. Unlike gen 1 or 2 , these 3rd generation= act on blood vessels .
    Non selective (B + A1 ) Carvedilol, Labetalol .
    B1 selective = nebivolol vasodilation by releasising Nitric Oxide from endotehelial cells.
    Betaxolol v .. by additionally blocking Calcium channels ( CCB)
    .. also can be applied to eye ,glaucoma, .
    9:50 Carvedilol and nebivolol have natioxidant properties (preferred for HF also alongside commonly prescribed with Bisoprolol and Metoprolol
    10:07 Intrinsic sympathomimetic properties (Pindolol, Acebutolol .
    Pindolol and Acebutolol not only block but also to weakly stimulate both Beta 1+2 receptors which leads to diminished effect on cardiac rate and output. These 2 are for pt who can't tolerate other Beta blockers because of pre existing bradycardia or heart block .

  16. this is crazy good and useful! I finally understand what all these alpha and beta things are in my pharm class. Thank you so so much!! Your video is simple, straight to the point and easy to follow and understand compared to all the other ones out there.

  17. These videos are amazing! If I had found them earlier in the semester I might have done better on my first Pharm exam! These videos break down 3 hours of lecture into something I can truly understand and you can bet I am using these videos for the rest of my nursing classes. Thank you so much! You are a Godsend and please keep it up!

  18. Thank you sooo much , it was clear , it was well explained and the pictures you put really helped keeping all the informations in mind thank you again

  19. Your videos have really helped me understand the concepts of Pharmacology..tysm…I have a request can you please make a video on anti-anginal drugs soon..?

  20. thank you so much. please make a video on Enzymes as drug targets ,Renal physiology, Physiology of hypertension and blood and vessels

  21. Any videos on defibrillation? I am curious how the heart can get resynced. Of course when a person collapses, but also any electrical therapy to gradually nudge the parts of the heart back into timing?

  22. Would 1st Generation or 3rd Generation beta blockers be more affective for Adrenaline and Generalized anxiety disorder. Weed threw me into an adrenaline hell for a while. Everyone says its your thoughts thats cause anxiety but when you’re naturally Tense fast heart rate and uneasy for no apparent reason its a huge hindrence

  23. I am on the lowest level beta blocker every other day for arrhythmia. Still makes my feet cold, but my hands don't cramp up anymore. Scary drugs. I hope research on NAD+ precursors advances fast. I read muscles tend to work much better when cell metabolism is enhanced.

Leave a Reply

Your email address will not be published.


*