**Core Concept**
Active drug transport refers to the movement of drugs across cell membranes against their concentration gradient, requiring energy expenditure. This process is crucial for the efficient delivery of essential nutrients and the elimination of waste products from the body.

**Why the Correct Answer is Right**
The correct answer involves the mechanism of active transport, which can be achieved through two main mechanisms: the sodium-potassium pump (Na+/K+-ATPase) and the proton-coupled transporters (e.g., OCT2 for cationic drugs). The sodium-potassium pump uses ATP hydrolysis to pump sodium ions out of the cell and potassium ions into the cell, creating a concentration gradient that can be utilized for the active transport of certain drugs. Proton-coupled transporters, on the other hand, use the electrochemical gradient of protons to facilitate the transport of drugs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it does not specify a valid mechanism of active drug transport.
**Option B:** This option might be incorrect because it does not accurately describe a well-established mechanism of active drug transport.
**Option C:** This option could be incorrect because it might refer to a passive transport mechanism, such as facilitated diffusion or simple diffusion.

**Clinical Pearl / High-Yield Fact**
The sodium-potassium pump is an essential component of the plasma membrane that helps maintain the resting membrane potential and regulates the concentration of sodium and potassium ions within the cell.

**Correct Answer:** A.