Midodrine and Guanfacine ER/Intuniv Confusion

[Miraclemaker11]

Dear Friends.  I’m hoping for some insight and help on this question.  My son has been taking Midodrine for his POTS and this seems to help increase his energy.  We are going to start him on Guanfacine ER tomorrow to help with his adrenaline surges/aggression.  Where I am confused is that both Midodrine and Guanfacine appear to be Alpha Receptor Agonist except that Midodrine constricts the blood vessels/raise blood pressure whereas Guanfacine dilates the blood vessels and presumably lowers blood pressure.  How is this possibly since both of these meds are alpha receptor agonists?  My son already has low (low 100s/low 60s) BP and we don’t want to make that worse but if this Guanfacine relaxes him and helps with the aggression then that would be a miracle.  Thank you so much for your help!

[Pistol]

@Miraclemaker11 here is what I found online: 

Guanfacine - Clinical Pharmacology. Guanfacine hydrochloride is an orally active antihypertensive agent whose principal mechanism of action appears to be stimulation of central α2-adrenergic receptors. By stimulating these receptors, Guanfacine reduces sympathetic nerve impulses from the vasomotor center to the heart and blood vessels. May 1 2019

 

Mechanism of Action: Midodrine hydrochloride forms an active metabolite, desglyMidodrine, that is an alpha1-agonist, and exerts its actions via activation of the alpha-adrenergic receptors of the arteriolar and venous vasculature, producing an increase in vascular tone and elevation of blood pressure.

So - the difference is that one stimulates alpha-1 receptors and the other stimulates alpha-2 receptors. Therefore they both have different actions. 

 

[Miraclemaker11]

As always Pistol, you are on target (pun intended).  This is so very helpful.  I figured that Guanfacine and Midodrine worked on different types of alpha receptors and this explains it best.  Thank you.  The next thing I’m wondering about is whether or not it makes sense for my son to take both Guanfacine and Midodrine simultaneously.  I really hope and pray that the Guanfacine helps with his aggression.  Here’s wishing you the very best in your quest for greater health (and humor).