Definition:

First-pass elimination: After the drug absorbed through the gastrointestinal biofilm enters the liver through the hepatic portal vein, the drug can be biotransformed under the action of liver drug enzymes. The degradation or inactivation of drugs before entering the systemic circulation is called "hepatic first-pass metabolism" or "hepatic first-pass effect". The greater the hepatic first-pass effect, the more the drug is metabolized, the lower the blood drug concentration and the drug effect will be significantly affected.