• Clinical science

Sympathomimetic drugs

Abstract

Sympathomimetics are substances that mimic or modify the actions of endogenous catecholamines of the sympathetic nervous system. Direct agonists directly activate adrenoceptors, while indirect agonists enhance the actions of endogenous catecholamines. α, β, and dopamine (D) receptors are stimulated 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” response).

Direct sympathomimetics
Drugs Action Indications

Albuterol (salbutamol), salmeterol

  • β2 > β1
Dobutamine
  • β1 > β2, α
Dopamine
  • D1 = D2 > β > α
Epinephrine
  • β > α
Fenoldopam
  • D1
Isoproterenol
  • β1 = β2
Midodrine
  • α1
  • Autonomic insufficiency
Norepinephrine
  • α1 > α2 > β1
Phenylephrine
  • α1 > α2

Ritodrine is the only FDA-approved drug for tocolysis during preterm labor but is no longer available in the US because of significant maternal and fetal side effects!

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

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

Effects

Organ System Receptors Sympathomimetic effect
Eye
  • α1

Bronchi

  • β2
  • Bronchodilation

Heart

  • β1

Blood vessels

  • α1
  • Contraction of renal and dermal vessels (primarily)
  • β2
  • Peripheral vasodilation

Gastrointestinal tract

  • α1
  • Sphincter contraction
  • β2
  • Peristalsis

Bladder

  • α1
  • Sphincter contraction
  • β2

Skeletal muscle

  • β2
  • ↑ Contraction
  • Glycogenolysis

Adipose tissue

  • β3
  • Lipolysis
Kidneys
  • β1

α and β 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 [2]

  • Tremor (most common side effect), agitation, insomnia, diaphoresis
  • Hypotension (due to peripheral vasodilation) and reflex tachycardia
  • Metabolic disturbances: hyperglycemia, hypokalemia

Indirect sympathomimetics

Side effects
Amphetamines
Cocaine
Ephedrine

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

β-blockers should be avoided in any person in which cocaine use is suspected, as the interaction between the drugs can lead to unopposed α-adrenergic activity!

References:[1][3][4]

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

last updated 12/17/2018
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