Pharm 101: Adenosine

Class

Antiarrhythmic

Pharmacodynamics

• Adenosine is a naturally occurring nucleoside
• As a bolus dose blocks AV nodal conduction and increases AV nodal refractory period due to:
  • Activation of inward rectifier K current
  • Inhibition of Ca current
  • Results in hyperpolarisation and suppression of calcium-dependent action potentials
• This interrupts re-entry pathway through AV node

Pharmacokinetics

• Very rapid metabolism by adenosine deaminase in red cells and endothelial wall
• Half-life < 10 seconds
• Duration of action ~ 30 seconds

Clinical uses

• Conversion of paroxysmal SVT to sinus rhythm:
  • Given via rapid IV bolus, proximal IV site
  • If initial dose ineffective, subsequent doses should be increased (no accumulation occurs)
• An uncommon variant of VT is adenosine-sensitive
• Will not be effective for SVT caused by adenosine-blockers such as theophylline

Adverse effects

• Short-lived
• Flushing 20%
• SOB or chest burning (likely bronchospasm-related) 10%
• Short-lived induction of high grade AV block
• AF
• Sense of impending doom

Precautions/contraindications

• Drug interactions:
  • Adenosine receptor blockers: theophylline, caffeine (reduce effectiveness)
  • Adenosine uptake inhibitors: dipyridamole (increases effectiveness)
  • Interaction with other AV nodal blocking drugs
• AV block
• Acute asthma

Further Reading

• Burns E. ECG Library: Supraventricular Tachycardia (SVT)
• Nickson C. Clinical Cases: Wide, Complex and Troublesome.