Pharm question - angina

[joe6102]

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Why are beta blockers contraindicated in variant (Prinzmetal) angina?

The only thing I can come up with is that they all have slight B2 antagonism that worsens the angina, but is that enough to offset the B1 blocking effects?

 

[Miami_med]

Why are beta blockers contraindicated in variant (Prinzmetal) angina?

The only thing I can come up with is that they all have slight B2 antagonism that worsens the angina, but is that enough to offset the B1 blocking effects?

I believe that is the reason. The solution to Prinzmetal is to get the smooth muscle in the Coronaries to relax. Even a mild antagonism to B2 will be VERY DETRIMENTAL. Also, since there is no actual blockage in Prinzmetal, it is my understanding that Nitrates will usually clear it up.

 

[tupac_don]

Why are beta blockers contraindicated in variant (Prinzmetal) angina?

The only thing I can come up with is that they all have slight B2 antagonism that worsens the angina, but is that enough to offset the B1 blocking effects?

Oh Yes.

 

[Dr.Phenomena]

I think it is because if you use Beta Blockers, you leave the alpha receptors unopposed.

 

[PharmD2MD]

I think it is because if you use Beta Blockers, you leave the alpha receptors unopposed.

Bingo! Remember that beta receptors generally cause vasodilation...primarily beta-2 in skeletal muscle. Beta-1 selective blockers are simply that- selective, but not completely specific for Beta 1.

Blocking beta receptors, alpha receptors on the vasculature are left unopposed...theoretically could cause a problem in someone with vasospastic angina. It's not really a big concern otherwise, unless you are treating a cocaine overdose or something along those lines.

 

[joe6102]

Bingo! Remember that beta receptors generally cause vasodilation...primarily beta-2 in skeletal muscle. Beta-1 selective blockers are simply that- selective, but not completely specific for Beta 1.

Blocking beta receptors, alpha receptors on the vasculature are left unopposed...theoretically could cause a problem in someone with vasospastic angina. It's not really a big concern otherwise, unless you are treating a cocaine overdose or something along those lines.

What I don't understand is this:
There are very few beta 2 receptors on the cardiac vasculature, and beta 1 agonists have very slight beta 2 activity, and yet this is enough to offset any potential gain from the decrease in myocardial O2 consumption. I just don't see it, unless doctors are just trying to avoid getting sued.

Whatever, I'll let it go. I don't have time to be looking up articles on it.

 

[PharmD2MD]

What I don't understand is this:
There are very few beta 2 receptors on the cardiac vasculature, and beta 1 agonists have very slight beta 2 activity, and yet this is enough to offset any potential gain from the decrease in myocardial O2 consumption. I just don't see it, unless doctors are just trying to avoid getting sued.

Whatever, I'll let it go. I don't have time to be looking up articles on it.

The coronary vasculature has beta-2 receptors in modest quantities as does skeletal muscle. Look at a Goodman and Gilmans if you need to prove it to yourself. Blockade of these receptors upsets the balance between constriction and vasodilation. Less vasodilation = more constriction. Myocardial O2 consumption isn't the primary problem to be addressed- it's myocardial O2 delivery. Fix the vasospasm, and the angina resolves. People with variant angina are probably more sensitive to these effects b/c they have heightened parasympathetic tone.

 

[deleted109597]

The unopposed alpha receptor concept is pretty theoretical, and most attendings I know dismiss it.
However, they don't use them in cocaine overdoses simply because there is so much "support" of it even as a Level C statement, that you wouldn't be able to stand on much in court if it came up.

 

[Dr. KMG]

B Blockers like 'propranolo' shoulden't be the treatment for 'angina' in most cases cuz they worsen the angina. I know that we can use them in very very special cases if we don't have any other available drug.