• Clinical science

Sympathomimetic drugs

Summary

Sympathomimetics are substances that mimic or modify the actions of endogenous catecholamines of the sympathetic nervous system. Direct agonists directly activate adrenergic receptors while indirect agonists enhance the actions of endogenous catecholamines. Sympathomimetics stimulate alpha-1 adrenergic receptors, beta-adrenergic receptors, and dopamine (D) receptors in various target tissues, such as the eyes, heart, and vascular smooth muscle. The clinical indications for sympathomimetics are broad and include asthma, heart failure, shock, and anaphylaxis. Side effects include hypertension, sinus tachycardia, and skeletal muscle tremor.

Overview

Sympathomimetic drugs mimic or enhance the actions of endogenous catecholamines of the sympathetic nervous system (fight-or-flight reaction).

Direct sympathomimetics

Direct sympathomimetics
Drugs Action Indications

Albuterol (salbutamol), salmeterol, terbutaline

  • β2 > β1
Clonidine
  • α2
Dobutamine
  • β1 > β2, α
Dopamine
  • D1 = D2 > β > α
Epinephrine
  • β > α
Fenoldopam
  • D1
Isoproterenol
  • β1 = β2
Methyldopa
  • α2
Midodrine
  • α1
Mirabegron
  • β3
Norepinephrine
  • α1 > α2 > β1
Oxymetazoline
  • α1 > α2
Phenylephrine
  • α1 > α2

DINED” is the acronym for examples of direct sympathomimetic drugs: D = Dopamine, I = Isoproterenol, N = Norepinephrine, E = Epinephrine, D = Dobutamine.

Indirect sympathomimetics

Indirect sympathomimetics increase the synaptic activity of endogenous catecholamines by increasing presynaptic release or inhibiting reuptake.

Indirect sympathomimetics
Drugs Action Indications
Indirect general agonist Reuptake inhibitor Releases catecholamines
Amphetamines

Cocaine
Ephedrine

References:[2][3][1][4][5]

Effects

Organ system Receptor Sympathomimetic effect
Eye
  • α1
  • α2
  • ↓ Aqueous humor production
  • β2
  • ↑ Aqueous humor production

Blood vessels

  • α1
  • α2
  • β2
  • Peripheral vasodilation → ↓ peripheral resistance → ↓ afterload

Heart

  • β1
  • Heart rate
  • ↑ Contractility
  • Automaticity and conduction velocity

Bronchi

  • β2
  • Bronchodilation

Gastrointestinal tract

  • α1
  • Sphincter contraction
  • β2
  • Peristalsis
Liver
  • α1
  • β2
Pancreas
  • α2
  • β2
Kidneys
  • β1
Bladder
  • α1
  • β2
  • β3
Female reproductive organs
  • β2
Male reproductive organs
  • α1

Skeletal muscle

  • β2
  • β3

Adipose tissue

  • α2
  • β1–3

Both alpha- and beta-adrenergic agonists are not fully selective at high doses!

References:[4][5]

Side effects

Direct sympathomimetics

Side effects
α1-agonists [6]
α2-agonists
β1-agonists

β2-agonists [3]

Indirect sympathomimetics

Side effects
Amphetamines
Cocaine
Ephedrine

Catecholamines (e.g., epinephrine, norepinephrine, isoproterenol, dopamine, dobutamine) should only be administered if monitored by an experienced physician! High-dose catecholamine administration requires intra-arterial blood pressure monitoring.

Beta blockers should be avoided in any person in which cocaine use is suspected because the interaction between the drugs can lead to unopposed activity of alpha-1 receptors.

References:[2][1][4]

We list the most important adverse effects. The selection is not exhaustive.

last updated 12/05/2019
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