Which of the following statements about first-pass metabolism is true?

First-pass metabolism refers to the initial metabolism of a drug when it is absorbed from the gastrointestinal (GI) tract and transported to the liver via the portal circulation. When a drug is taken orally, it is first absorbed through the intestinal lining in the small intestines. Upon absorption, it enters the portal vein and is directed to the liver before it reaches systemic circulation. In the liver, the drug can undergo extensive metabolism, which may reduce its bioavailability, or the amount of active drug that reaches the systemic circulation.

This process is particularly significant for drugs that have low oral bioavailability due to high first-pass metabolism. Understanding this concept is crucial for healthcare providers, as it influences dosing regimens and the formulation of drugs.

Other options presented do not accurately describe first-pass metabolism. For example, intramuscular injections bypass the GI tract, so those drugs do not undergo first-pass metabolism. Similarly, while there can be metabolism occurring in the intestines, it is more accurately described as metabolic degradation or bacterial metabolism rather than first-pass metabolism. The dermis does not function the same way as the liver in metabolizing drugs from transdermal patches; rather, absorption occurs directly into the systemic circulation. These distinctions highlight the uniqueness of first-pass metabolism associated