Epinephrine Pharmacology!

Epinephrine Pharmacology

Also known as adrenaline, epinephrine is an important medicine used in the treatment of often life-threatening conditions. Here, we review the must-know pharmacology of epinephrine that you need to know.

Epinephrine is a hormone produced from the adrenal glands as well as from certain neurons, where it acts as a neurotransmitter. Epinephrine is responsible for “flight or fight” effects such as:

• increased blood flow to muscles
• pupillary dilation
• increased cardiac output
• raised blood sugar levels

Clinically, epinephrine is used in the treatment of conditions such as:

• Allergic reactions / Anaphylaxis – where epinephrine is used to tackle the allergic response caused by stings, medicines, contrast agents, or any other known triggers.
• Cardiac arrest – epinephrine is routinely used as part of ALS, advanced life support, algorithms.
• Local anesthesia – epinephrine is used to prolong the effects of local anesthetics – such as bupivacaine and lidocaine. Epinephrine acts as a vasoconstrictor, reducing the absorption of the anesthetic and prolonging its effects.
• Hypotension caused by septic shock
• Acute asthma attacks – though direct-acting beta-2 agonists are the preferred treatment choice, epinephrine may be used in cases where standard treatment protocols have proven insufficient.

Let’s now turn our attention to how epinephrine works to achieve these therapeutic effects.

Mechanism of action

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

• Beta-1 receptors – increase in heart rate, contractility, and excitability. These effects render epinephrine useful in cardiac arrest where the drug causes the redistribution of blood flow to the heart and helping to restore heart rhythm.
• Beta-2 receptors – bronchodilation; suppression of the release of inflammatory mediators.
• Alpha-1 receptors – vasoconstriction of blood vessels supplying skin and mucosa.
• Alpha-2 receptors – inhibits insulin release; induces pancreatic glucagon release.

The beta-2 effects are vital in the treatment of 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

Common side effects with epinephrine include:

• Shakiness
• Anxiety
• Sweating
• Tachycardia
• Hypertension
• Palpitations
• Panic attacks
• Pale skin
• Dizziness
• Headache
• Weakness

A small number of patients may experience abnormal heart rhythms, acute pulmonary edema, and – in very rare cases – epinephrine has been linked to Takotsubo cardiomyopathy.

However, epinephrine increases the risk of serious cardiovascular events in patients with established heart disease.

Clinical Pharmacology

Clinical pharmacology factors to consider about epinephrine include:

• That for cardiac arrest and anaphylaxis, there are no contraindications against its use. Epinephrine is commonly administered every 3-5 minutes in cardiac arrest.
• Epinephrine use is often dangerous and its effects must be balanced against the target clinical benefits. In cases of cardiac arrest, for example, epinephrine treatment can lead to adrenaline-induced hypertension. Severe hypertension may also occur if epinephrine is taken alongside a non-selective beta-blocker.
• That, due to its vasoconstrictive effects, epinephrine should be used with caution in patients with heart disease.
• Combination preparations of epinephrine and a local anesthetic should not be administered to parts of the body that have poor collateral blood supply – for example, toes and fingers – where epinephrine can cause tissue necrosis.
• In life-threatening situations, such as anaphylaxis, epinephrine is administered first and then later prescribed. Epinephrine is available as an auto-injector which is administered into the anterolateral aspect of the thigh, every 5-minutes if necessary.
• Typical adult doses in the treatment of cardiac arrest include:
  Injectable Solution of 0.1 mg/mL (1:10,000):
  IV: 0.5-1 mg (5-10 mL) IV once; during resuscitation effort, 0.5 mg (5 mL) should be administered IV every 5 minutes thereafter.
  Intracardiac: 0.3-0.5 mg (3-5 mL) into left ventricle once only, performed by a specialist with experience in this technique.
  Endotracheal: 0.5-1 mg (5-10 mL) via endotracheal tube directly into the bronchial tree once.

That’s about it for our study of epinephrine pharmacology. Check back to our pharmacy blog soon for more exclusive content to help you master the science of drugs and medicines!