What are the typical effects of enterohepatic recirculation on the concentration-time profile?

• A. Shortens half-life and causes a single sharp peak
• B. Eliminates first-pass metabolism
• C. Creates secondary peaks, prolongs apparent half-life, and extends drug exposure
• D. Reduces overall exposure

Answer: (C)

Enterohepatic recirculation is when drug molecules that are excreted into bile are released back into the gut and then reabsorbed into the bloodstream. This reentry acts as a second input of drug after the initial absorption, which often shows up as a second peak on the concentration-time curve. Because the drug returns to systemic circulation after biliary excretion, the apparent elimination half-life is longer and the overall exposure (AUC) is extended due to these additional absorption cycles. The timing and size of the secondary peak depend on how quickly bile is released, gut transit, and whether gut bacteria can cleave conjugates to regenerate the active drug. So, enterohepatic recirculation creates secondary peaks, prolongs the apparent half-life, and extends drug exposure. It does not eliminate first-pass metabolism, and it can increase exposure rather than reduce it, through recycling.