Which of the following is a P-glycoprotein inhibitor
**Core Concept**
P-glycoprotein (P-gp) is a transmembrane protein that acts as a efflux pump, playing a crucial role in limiting the absorption and distribution of various endogenous compounds, xenobiotics, and chemotherapeutic agents. P-gp is primarily expressed in the blood-brain barrier, liver, kidneys, and intestines, where it helps to maintain cellular homeostasis and prevent the accumulation of potentially toxic substances.
**Why the Correct Answer is Right**
Rifampicin (A) is a well-known inhibitor of P-glycoprotein. By binding to P-gp, rifampicin reduces its efflux activity, thereby increasing the intracellular concentration of various substrates, including chemotherapeutic agents. This action is particularly relevant in the context of cancer treatment, where P-gp inhibitors like rifampicin can enhance the efficacy of chemotherapeutic agents by reducing their efflux from cancer cells.
**Why Each Wrong Option is Incorrect**
* **Option B:** Cyclosporin is actually an inhibitor of the multidrug resistance-associated protein 2 (MRP2), not P-glycoprotein.
* **Option C:** Verapamil is a partial P-gp inhibitor but is not as potent as rifampicin in inhibiting P-gp activity.
* **Option D:** Ketoconazole is primarily an inhibitor of cytochrome P450 3A4 (CYP3A4) and has minimal effect on P-glycoprotein.
**Clinical Pearl / High-Yield Fact**
P-glycoprotein inhibitors like rifampicin can increase the risk of drug interactions and toxicity, particularly when used in combination with other medications that are substrates or inhibitors of P-gp. Clinicians should carefully monitor patients receiving P-gp inhibitors for signs of toxicity and adjust dosages accordingly.
**Correct Answer: A. Rifampicin**