The in vivo process of drug includes: absorption, distribution, metabolism-transport, excretion-elimination. Absorption: Absorption of drugs is a necessary process for drugs to enter the blood circulation from the site of drug administration, and mostly belongs to passive transport. Distribution: The process of transferring drugs to tissues and organs through blood is called distribution, and the distribution process of drugs also belongs to passive transfer. The distribution of drugs in the body is often in dynamic equilibrium and often unevenly distributed. Biotransformation: The drug undergoes chemical structural changes in the body under the action of drug enzymes, mainly in the liver. Excretion: The process of excretion of drugs and their metabolites from the body. The main excretory organs are: kidney, liver, gastrointestinal tract and lungs, followed by sweat and milk.