Antiarrhythmics: adenosine interactions: practice question

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Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Reduce the initial dose, because dipyridamole blocks adenosine reuptake and prolongs its action

Adenosine has a half-life of seconds because it is taken up into red cells and endothelium by nucleoside transporters. Dipyridamole blocks this uptake, which potentiates and prolongs adenosine, so a much smaller dose is used to avoid prolonged asystole. Methylxanthines such as theophylline and caffeine have the opposite effect by antagonising adenosine receptors.

Option by option

• A. Reduce the initial dose, because dipyridamole blocks adenosine reuptake and prolongs its action (correct)

  Correct. Blocked reuptake extends the action of adenosine, so a lower dose is safer.

• B. Avoid adenosine and give intravenous digoxin instead

  Digoxin is slower and less effective for abrupt termination, and the interaction can be managed with dose reduction.

• C. Increase the dose, because dipyridamole upregulates adenosine receptors

  Dipyridamole does not upregulate receptors; it blocks nucleoside uptake.

• D. Give the usual dose, because dipyridamole acts only on platelets

  Dipyridamole potentiates adenosine through nucleoside transport inhibition, not only through platelets.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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