Which of the following drugs may enhance the effect of warfarin and increase the risk of bleeding?
**Core Concept**
Warfarin is an anticoagulant that inhibits vitamin K-dependent clotting factors in the liver, thereby prolonging bleeding time. Enhancing its effect increases the risk of bleeding, particularly in patients with pre-existing coagulopathy or those at high risk of falls.
**Why the Correct Answer is Right**
The correct answer is a drug that either inhibits platelet aggregation, enhances warfarin's anticoagulant effect, or has a synergistic effect with warfarin. This results in an increased risk of bleeding due to the additive effects on coagulation pathways. **Aspirin**, for example, irreversibly inhibits COX-1, thereby reducing thromboxane A2 production, which is essential for platelet aggregation. When combined with warfarin, the risk of bleeding increases due to the additive anticoagulant effects.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not have a well-documented interaction with warfarin that increases the risk of bleeding.
* **Option B:** This option is incorrect because it may actually decrease the effect of warfarin by reducing its absorption or enhancing its metabolism.
* **Option D:** This option is incorrect because it is not commonly used in clinical practice and does not have a well-documented interaction with warfarin.
**Clinical Pearl / High-Yield Fact**
When prescribing warfarin, always check for potential interactions with other medications, particularly those that inhibit platelet aggregation or enhance warfarin's anticoagulant effect. Regular monitoring of INR is essential to prevent bleeding complications.
**Correct Answer:** A. Aspirin