Pharmacology of Epinephrine

Epinephrine is used in cases of cardiac arrest, in anaphylaxis and to prolong the effects of local anesthetics. Here, we review its indications, mechanism of action, side effects and drug interactions – establishing its wider role in medicine.

Epinephrine (adrenaline) is a serious medicine used in many serious clinical contexts.

It is a hormone, produced from the adrenal glands and in certain neurons. It’s responsible for many “flight or fight” effects – increasing blood flow to muscles, causing pupillary dilation, increasing cardiac output and raising blood sugar levels.

In a clinical context, epinephrine has the following uses:

  • Anaphylaxis – epinephrine is used to address the allergic response caused by stings, medicines, contrast agents or any other known triggers.
  • Cardiac arrest – where it increases survival and return of spontaneous circulation (ROSC).
  • Local anesthesia – it is used to prolong the effects of local anesthetic drugs, such as bupivacaine and lidocaine. For example – it is used alongside local anesthetics as a vasoconstrictor, reducing absorption of the anesthetic to prolong its effects.

It has also been used to treat asthma, though it has since been superseded by more direct-acting drugs, such as beta-2 agonists.

Mechanism of action

The panoply of “flight or fight” effects are mediated through epinephrine agonism at:

  • Beta-1 receptors – increase in heart rate, contractility and excitability etc.
  • Beta-2 receptors – bronchodilation; suppression of inflammatory mediator release
  • Alpha-1 receptors – vasoconstriction of blood vessels supplying skin, mucosa etc.
  • Alpha-2 receptors – inhibits insulin release; induces glucagon release from the pancreas

The beta-2 effects are paramount in treating anaphylaxis.

Anaphylaxis leads to hypotension, vasodilation and bronchoconstriction.

Agonism at beta-2 receptors leads to bronchodilation and suppression of inflammatory mediator release from mast cells – reducing inflammation and promoting bronchodilation.

Side effects

Side effects with epinephrine include:

  • Shakiness
  • Anxiety
  • Sweating
  • Tachycardia
  • Hypertension
  • Palpitations
  • Panic attacks

Epinephrine increases the risk of serious cardiovascular events in patients with established heart disease.

Clinical considerations

When we talk about the clinical pharmacology of epinephrine, we need to think about the following factors:

  • That severe hypertension may occur if epinephrine is taken alongside a non-selective beta-blocker.
  • That for cardiac arrest and anaphylaxis, there are no contraindications against its use. Epinephrine is commonly administered every 3-5 minutes in cardiac arrest.
  • That epinephrine should be used with caution in patients with heart disease due to its vasoconstrictive effects.

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