Alpha and Beta Receptors

Alpha and Beta Receptors

March 1, 2024

Have you ever had the opportunity to hear the Cleveland Orchestra? Maybe you have had the opportunity to attend a school band concert to see one of your children, nephews, or nieces? Even for those who are not music fans, it is amazing to listen to how the different groups all work together, meshing every component from brass to percussion to woodwinds!

What might be the most interesting component of an orchestra or band is the influence of the conductor. He or she can adjust the speed of the entire group or adjust the volume of specific sections. In a similar way, medications can have systemic effects on the entire body or just local targeted effects. This can be accomplished because individual receptors respond to different drugs. 

Certain drugs can either excite (agonist) or block (antagonist) what the organ is designed to do. Some drugs tend to work on the sympathetic (adrenergic) nervous system (fight or flight), while others concentrate on the parasympathetic system (rest and restore). Finally, drugs can also be grouped as Alpha, Beta 1, or Beta 2, based on what organs they work on. You might remember “Alpha for Arteries, Beta 1 for 1 heart, Beta 2 for 2 lungs”. 

This concept may seem very complicated, but when you break it down, it all makes sense. Take Epinephrine, for example. It is your most popular adrenergic (sympathetic) agonist (encourager). It excites Alpha (vasoconstriction), Beta 1 (increased heart rate and strength), and Beta 2 (bronchodilation) receptors for a massive systemic response. It is exactly what we want to happen in drastic situations like cardiac arrest or anaphylactic reactions. Sometimes, we want it to hit the entire system fast (0.1mg/ml IV/IO) or sometimes a little slower (1.0 mg/ml IM) filtered through the deltoid. Other times, we want to target specific tissue, such as in stridor (Racemic Epi nebulized), and minimize systemic effects. Because every person is different and can have varying degrees of something like cardiogenic or septic shock, in those cases, it is better if your Epi administration is titrated (adjusted) to achieve your goals (10 mcg/ml of Push Dose Epi, 1-5 ml or up to 50mcg per dose if needed).

Other medications can be identified in similar ways. Suppose your patient has been prescribed Metoprolol/Lopressor to fight hypertension. You probably recognize the “lol” as being a beta blocker. Metoprolol is considered a Beta 1 adrenergic antagonist, meaning it will slow down the rate and reduce the contractile force of the heart while not affecting the lungs. Your protocol allows the use of Metoprolol for rate control in narrow complex tachycardia. Because of the potential danger involved, it is a medication that requires medical approval prior to administration. But your drug box also contains Labetolol/Trandate. This beta blocker is nonselective, which means all Alpha and Beta receptors respond to it. We only use this in eclampsia, preeclampsia, or post-partum hypertension, and it, too, is red-boxed. You can see why it is so important to make sure you do not confuse the two. 

Pharmacology at the EMS level is not out of your grasp of understanding. Next time you see medications listed as adrenergic, antagonistic, or Beta 2, simply break it down to what it means. And when you see an unfamiliar word, take a second to look it up!

Till next time, stay safe!


The UH EMS-I Team

University Hospitals