The phrase "first-pass hepatic metabolism" refers to:

First-pass hepatic metabolism is a crucial pharmacokinetic concept concerning how drugs are processed in the body. When a drug is administered, particularly via oral ingestion, it travels through the gastrointestinal tract and then is absorbed into the bloodstream. Before the drug can circulate throughout the body and exert its therapeutic effects, it first passes through the liver via the portal vein.

During this initial passage, the liver metabolizes the drug, and this process can significantly reduce the amount of the active drug that enters systemic circulation. This reduction decreases the drug's bioavailability, which is defined as the proportion of a drug that reaches the systemic circulation unchanged and is available to have an effect.

The other options do not accurately capture the concept of first-pass metabolism. For instance, while some drugs may undergo complete inactivation in the liver, this is not a general rule, as many drugs are merely metabolized to less active or inactive forms, not always rendered completely inactive. Additionally, the notion of alternate metabolism to an active form does occur in some contexts, but it does not describe the primary function of first-pass metabolism. Lastly, stating that all drugs are eliminated via the liver is an oversimplification; many drugs are eliminated or metabolized by other organs as well, and