What is the function of P-glycoprotein (PGP) in drug absorption?

P-glycoprotein (PGP) is an important efflux transporter that plays a significant role in drug absorption and disposition. Its primary function is to actively transport a variety of substrates, including many pharmaceuticals, out of cells. This action can effectively reduce the concentration of drugs within cells, thereby decreasing their bioavailability and absorption from the intestinal lumen into systemic circulation.

When PGP actively exports drugs from enterocytes (the cells lining the intestinal wall) back into the intestinal lumen, it can hinder the absorption of those drugs. Essentially, while drugs may be present in the gastrointestinal tract, PGP limits the amount that enters the bloodstream by preventing them from remaining within the enterocyte or passing into circulation. This function is crucial for the body's defense against potentially harmful compounds, as PGP can also transport toxins and xenobiotics out of cells. Thus, when considering the involvement of PGP in drug absorption, its ability to export drugs from cells is a key mechanism that can reduce overall absorption.

This clarification about the role of P-glycoprotein highlights why the answer regarding its effect on drug export and absorption is accurate.