Opioids · Pharmacology

Why is Codeine often considered a 'prodrug'?

  1. It must be converted to morphine by CYP2D6 to relieve pain
  2. It is only active in the acidic environment of the stomach
  3. It is absorbed only through the skin and mucous membranes
  4. It binds to receptors only after it is excreted in the bile
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Correct answer: It must be converted to morphine by CYP2D6 to relieve pain

Codeine itself has very low affinity for opioid receptors. Its analgesic potency depends on its metabolic conversion to morphine by the polymorphic enzyme CYP2D6; 'ultra-rapid metabolizers' are at risk of morphine toxicity from standard codeine doses.

Difficulty: Medium Question 14 of 20

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