In Vivo PK

       First Pass Effect refers to the phenomenon where the bioavailability of a drug decreases after liver metabolism. After oral administration, the drug first enters the intestines, then is absorbed into the bloodstream, and then enters the liver through the portal vein. In the liver, the drug is metabolized by hepatocytes and some of it is converted to metabolites and excreted. This process will lead to a decrease in the bioavailability of the drug.  

       In first pass effect analysis, researchers will evaluate the first pass effect of drugs by comparing their bioavailability across different administration routes, such as oral and intravenous injection. If the bioavailability of the drug during oral administration is significantly lower than that during intravenous injection, it can be considered that the drug has a significant first pass effect.

       First pass effect analysis can help researchers better understand the metabolism and absorption of drugs in vivo, and provide important basis for preclinical drug development. For example, if a drug has a significant first pass effect, clinicians may need to adjust the dosage or choose other routes of administration to ensure that patients receive treatment safely and effectively.