## Core Concept
The displacement of a protein-bound drug refers to a phenomenon where one drug displaces another drug from its binding sites on plasma proteins, such as albumin. This concept is crucial in pharmacology as it affects the drug's distribution, efficacy, and potential for toxicity. Protein binding is a reversible process, and the bound drug is pharmacologically inactive.

## Why the Correct Answer is Right
The correct answer, , implies that the displacement of a protein-bound drug increases the free fraction of the displaced drug. When a drug is displaced from plasma proteins, more of the drug becomes available in its free (unbound) form. This can lead to an increase in the drug's pharmacological effects or toxicity because only the free fraction of a drug is pharmacologically active. The mechanism involves competition between drugs for binding sites on plasma proteins.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because displacement of a protein-bound drug does not decrease the free fraction of the drug; rather, it has the opposite effect.
* **Option B:** This option is incorrect as displacement does not primarily affect the drug's elimination half-life directly; it affects the drug's availability and activity.
* **Option C:** Although not explicitly listed, if an option suggested no change or a decrease in pharmacological effect, it would be incorrect because displacement typically increases the pharmacological effect or potential for toxicity.

## Clinical Pearl / High-Yield Fact
A key point to remember is that drugs with high protein binding (> 80-90%) are more likely to be involved in drug displacement interactions. For example, warfarin, a highly protein-bound anticoagulant, can be displaced by other drugs like phenylbutazone, leading to increased anticoagulant effect and risk of bleeding.

## Correct Answer: D.