Pharmacology of Adenosine

Adenosine is an important cardiovascular medicine used in the treatment of arrhythmias. However, the drug also comes with a range of significant adverse effects and warnings.

Here, we review those fundamental facts about adenosine pharmacology that you need to know – focussing on indications, mechanism, side effects and drug interactions.

Let’s gets started.

Indications

Adenosine is used in the treatment of supraventricular tachycardia – a first-line agent in the treatment of this type of arrhythmia.

More specifically, adenosine can be used to treat re-entrant arrhythmias that require the AV node. Examples include AV re-entrant tachycardia (AVRT) and AV nodal re-entrant tachycardia (AVNRT).

Adenosine is not used for atrial arrhythmias – such as atrial fibrillation and atrial flutter – that do not use the AV node for re-entrancy.

Mechanism of action

Adenosine is sometimes classified as a class V antiarrhythmic drug.

Its mechanism of action can be summarised as follows:

  • Adenosine acts as an agonist at adenosine receptors of the heart; G-protein coupled receptors.
  • This has two effects. First, it reduces the number of spontaneous depolarisations (automaticity) and, second, it enhances depolarisation resistance (refractoriness).
  • These two effects slowly reduce sinus rate, cardiac conduction velocity and increases AV node refractoriness. By increasing AV node refractoriness, adenosine works to break re-entry circuits that are often implicated in causing supraventricular tachycardias.

Adenosine is taken up very rapidly. It has a plasma half-life of fewer than 10 seconds. This impacts the site of administration (see below).

Side effects

Adenosine is associated with the following side effects:

  • Bradycardia
  • Nausea
  • Headache
  • Neck / jaw discomfort
  • Asystole
  • Breathlessness
  • Sweating
  • Facial flushing
  • Metallic taste

Due to transient asystole, patients often experience a sense of “impending doom”. However, this effect is transient and passes quite rapidly.

Some patients experience a temporary chest rash.

Clinical considerations

Here are some of the major clinical factors of adenosine that you need to know:

  • Adenosine is contraindicated for use in patients with asthma / COPD, severe hypotension or in cases of decompensated heart failure. In the case of asthma and COPD, adenosine has the potential to induce bronchospasm.
  • Dipyridamole blocks uptake of adenosine into cells, meaning that the effects of adenosine become more prolonged.
  • Other drugs – such as caffeine, theophylline – are competitive antagonists at adenosine receptors and so higher doses of adenosine may be required.
  • The standard dose of adenosine is 6mg IV. If ineffective, a 12mg dose may be administered.
  • Since adenosine is rapidly taken up by cells, the IV dose should be administered as proximally as possible (for example: antecubital fossa) using a large-bore cannula. Once administered, it should be followed by a 0.9% NaCl flush.

Adenosine remains an important medicine in cardioversion – restoring abnormal heart rhythms. However, use of the medicine comes with significant risks and challenges. The medicine should only be administered by a clinician experienced in its use. Close monitoring is required in all cases.

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