## **Core Concept**
The question tests knowledge of oral anticoagulants, specifically their duration of action. Oral anticoagulants are crucial in the management and prevention of thromboembolic disorders. They primarily work by inhibiting the synthesis of vitamin K-dependent clotting factors.

## **Why the Correct Answer is Right**
The correct answer, **Phenindione**, is a long-acting oral anticoagulant. However, it's more accurate to discuss the commonly known long-acting oral anticoagulant, **Phenindione** is less commonly referenced but **Warfarin** is a well-known long-acting anticoagulant with a half-life that can range approximately from 20 to 60 hours, allowing for once-daily dosing.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although specific drugs aren't named, options like Aspirin have a short duration of action and aren't classified as oral anticoagulants in the traditional sense of affecting vitamin K-dependent factors.
- **Option B:** This option is incorrect as it does not specify a drug known for long-acting properties compared to the correct answer.
- **Option D:** This option is incorrect because it does not represent a drug known for its long-acting anticoagulant effects.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **Warfarin**, a commonly used oral anticoagulant, has a long half-life which allows for once-daily dosing and it takes about 5-7 days for its full effect to be realized due to the half-lives of the clotting factors it inhibits.

## **Correct Answer:** D. Phenindione