Rifampicin's effect on P-gp expression is to:

Rifampicin's effect on P-gp expression is to:

• A. Increases P-gp and reduces absorption
• B. Decreases P-gp and increases absorption
• C. No effect on P-gp
• D. Inhibits P-gp activity

Answer: (A)

Rifampicin activates the pregnane X receptor (PXR), which upregulates the MDR1 gene that encodes P-glycoprotein. This increases the amount of P-gp in tissues like the intestinal lining, leading to more drug being pumped back into the lumen as it tries to be absorbed. The outcome is lower oral bioavailability for P-gp substrates because their absorption is actively reduced by higher efflux. This induction effect takes some time with continued rifampicin therapy, explaining why absorption of drugs such as digoxin can decrease when rifampicin is present. The other options describe inhibition or no effect, which doesn’t match rifampicin’s role as a P-gp inducer.

Rifampicin activates the pregnane X receptor (PXR), which upregulates the MDR1 gene that encodes P-glycoprotein. This increases the amount of P-gp in tissues like the intestinal lining, leading to more drug being pumped back into the lumen as it tries to be absorbed. The outcome is lower oral bioavailability for P-gp substrates because their absorption is actively reduced by higher efflux. This induction effect takes some time with continued rifampicin therapy, explaining why absorption of drugs such as digoxin can decrease when rifampicin is present. The other options describe inhibition or no effect, which doesn’t match rifampicin’s role as a P-gp inducer.