H2 Blockers · Pharmacology

A patient is taking Cimetidine along with Warfarin. What is the most likely outcome for the patient's INR?

  1. The INR will decrease, raising the clot risk
  2. The INR will rise, increasing bleeding risk
  3. The INR will remain essentially unchanged
  4. The INR will become dangerously unstable
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Correct answer: The INR will rise, increasing bleeding risk

Cimetidine inhibits the metabolism of S-warfarin (the more potent isomer) via CYP2C9. This leads to higher warfarin levels and an elevated INR, putting the patient at risk for bleeding.

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