Figure 2.

First‐pass metabolism of orally ingested medications. The drug enters the liver via the portal vein, becomes bioavailable after metabolism in the liver into active metabolites, and then enters systemic circulation via the hepatic vein. In patients with liver disease, impaired hepatic function, reduced hepatic blood flow, and portosystemic shunting reduce first‐pass metabolism, thereby increasing the proportion of drug that is bioavailable and increasing the risk for toxicity.