My heart began to race, then I....

The concern with Inderal (Rx for blood pressure) is not with amide local anesthetics but with epinephrine. This is the body's response to perceived threat or danger. During this reaction, certain hormones like adrenalin and cortisol are released, speeding the heart rate, slowing digestion, shunting blood flow to major muscle groups, and changing various other autonomic nervous functions, giving the body a burst of energy and strength. The interaction is as follows:

As you know, there are two main classes of beta blockers - cardioselective and non-cardioselective. The cardioselective beta blockers block only the beta-1 receptors (those responsible for making the heart beat faster and more forcefully) but leave the beta-2 receptors open. The non-cardioselective beta blockers block both beta-1 and beta-2 receptors (those responsible for peripheral vasodilation and other effects).
Also, as you know, epinephrine is an adrenergic activist, stimulating alpha, beta-1 and beta-2 receptors.
If someone is taking a cardioselective beta blocker and are given moderate to high doses of epinephrine in the local anaesthetic, the epinephrine will want to stimulate both beta receptors but the beta-2 receptors are the only ones that are open. This is good because the heart will not beat faster and more forcefully (the beta-1 receptors are blocked) but beta-2 mediated activation by the epi will cause vasodilation as usual. This vasodilation will counteract alpha mediated vasoconstriction. (which is undesirable from a CVS perspective). So the end result is no major effect on the patients cardiovascular system.
However if the patient is taking a non-cardioselective beta blocker (eg Inderal), both beta-1 and beta-2 receptors are blocked and so if they receive a moderate to high dose of epi, epi can not stimulate either beta receptor. All that happens is the alpha mediated vasoconstriction and this results in a rise in blood pressure (no counteracting beta-2 mediated vasodilation can occur) and to make matters worse, the patient will characteristically have a low pulse due to being on a beta blocker. Low pulse and rising blood pressure is obviously a bad combination.

Comments to author. localanesthetics@yahoo.ca M.Sc. PharmD. CCPE Please visit WWW.AnestheticsNews.com

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