Nursing Pharmacology: Autonomic Pharmacology Adrenergic Drugs
α1 Selective Adrenergic Agonists
α1 selective adrenergic agonists activate α adrenergic receptors in vascular smooth muscle producing vasoconstriction.
Peripheral vascular resistance is increased.
Blood pressure may be increased, causing a reflex reduction heart rate
α1 adrenergic agonists are used clinically in management of hypotension and shock.
Phenylephrine (Neo-Synephrine) and methoxamine (Vasoxyl) are direct-acting vasoconstrictors.
Mephentermine (Wyamine) and metaraminol (Aramine) act both by direct receptor activation and by promoting epinephrine release (indirect activity).
Methoxamine is a specific α1 receptor agonist and as such both:
Increases peripheral resistance and
Causes an increase in blood pressure that precipitates sinus bradycardia (decreased heart rate) due to vagal reflex.
Reflex bradycardia may be blocked by atropine (muscarinic antagonist)
Clinical uses include management of hypotensive states and termination (by vagal reflex) of paroxysmal atrial tachycardia (adenosine or other agents may be preferable)
Hoffman, B.B and Lefkowitz, R.J, Catecholamines, Sympathomimetic Drugs, and Adrenergic Receptor Antagonists, In, Goodman and Gillman's The Pharmacologial Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) TheMcGraw-Hill Companies, Inc.,1996, pp.216-219.