**Core Concept**
High plasma protein binding of a drug refers to the phenomenon where a significant portion of the drug molecules binds to plasma proteins, such as albumin, in the bloodstream. This binding reduces the amount of free (unbound) drug available for renal excretion and metabolism.

**Why the Correct Answer is Right**
When a drug is highly bound to plasma proteins, it is less likely to be filtered by the kidneys, as the bound fraction is not freely available in the plasma. As a result, the glomerular filtration rate (GFR) of the drug decreases, leading to a reduced rate of excretion. This is because the kidneys primarily filter the unbound or free fraction of the drug. The bound fraction remains in the bloodstream and is not readily available for excretion.

**Why Each Wrong Option is Incorrect**
**Option B:** High volume of distribution is actually associated with lipophilic drugs that penetrate tissues easily, not with high plasma protein binding.

**Option C:** High plasma protein binding can actually increase the duration of action of a drug, as the bound fraction is not readily available for metabolism or excretion.

**Option D:** High plasma protein binding can lead to increased drug interactions, as the bound drug can displace other tightly bound drugs from their binding sites, leading to changes in their plasma concentrations.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that high plasma protein binding can affect the pharmacokinetics of a drug, particularly its renal excretion and duration of action.

**Correct Answer:**
✓ Correct Answer: A. Decreased glomerular filtration.