This document discusses first pass metabolism, which refers to the process by which orally administered drugs are metabolized by the liver before reaching systemic circulation. It notes that drugs administered enterally must pass through the liver, where some portion may be metabolized and inactivated before having a systemic effect. The document then provides an overview of the key steps in first pass metabolism, including proximal tubular secretion and distal tubular reabsorption in the kidneys, which can also impact drug bioavailability.