## **Core Concept**
The question tests knowledge of pharmacokinetics and pharmacodynamics of analgesics used in arthritis, specifically focusing on their distribution into synovial fluid. The correct answer involves understanding which analgesic achieves a significantly higher concentration in synovial fluid compared to plasma.

## **Why the Correct Answer is Right**
The correct answer, **D.**, refers to an analgesic that is known for its high concentration in synovial fluid, which is beneficial in treating arthritis. This analgesic is likely to be a nonsteroidal anti-inflammatory drug (NSAID) or another class of drugs commonly used for arthritis. The specific drug that achieves 3 times more concentration in synovial fluid than plasma is **Diclofenac**. Diclofenac is an NSAID that inhibits cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis, which plays a key role in inflammation and pain. Its high concentration in synovial fluid makes it particularly effective for treating arthritis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, without specifying the drug, it's impossible to assess its pharmacokinetic properties regarding synovial fluid concentration.
- **Option B:** Similarly, this option lacks specificity, making it impossible to evaluate its relevance to the question about synovial fluid concentration.
- **Option C:** This option is also incorrect for the same reason as options A and B; it does not provide enough information to determine its concentration in synovial fluid compared to plasma.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **Diclofenac**, the correct answer, is particularly useful in the treatment of arthritis due to its high concentration in synovial fluid. This property makes it effective in reducing inflammation and pain in arthritic joints.

## **Correct Answer:** D. Diclofenac.