Decreased effect of warfarin is seen in case of :
**Core Concept**
Warfarin is an anticoagulant that acts by inhibiting the production of vitamin K-dependent clotting factors in the liver. Its effect can be influenced by various factors, including genetic variations, diet, and concurrent medications.
**Why the Correct Answer is Right**
Warfarin is a substrate of the enzyme CYP2C9, which is involved in its metabolism. Genetic polymorphisms in the CYP2C9 gene can lead to decreased enzyme activity, resulting in higher warfarin levels and increased risk of bleeding. Individuals with the CYP2C9*2 or CYP2C9*3 genotypes may require lower doses of warfarin to achieve the same anticoagulant effect.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while liver disease can affect warfarin metabolism, it is not the primary reason for decreased warfarin effect. Liver disease may lead to increased warfarin levels due to impaired metabolism, but it is not directly related to the genetic factors mentioned.
**Option B:** This option is incorrect because vitamin K supplementation can actually reverse the anticoagulant effect of warfarin, rather than decreasing its effect.
**Clinical Pearl / High-Yield Fact**
Genetic testing for CYP2C9 polymorphisms can help guide warfarin dosing and reduce the risk of bleeding in patients taking this medication. This is particularly important for individuals with a history of bleeding or those taking other medications that interact with warfarin.
**Correct Answer:** C.