The in vivo process of drug includes absorption, distribution, metabolism and excretion. The absorption of drug refers to the process of drug molecules passing through the cell membrane and entering the blood circulation from the site of drug use, and most of them are passive transport. There are many factors affecting absorption, and the rate of absorption varies with different drug formulations. The distribution of drugs refers to the transportation of drugs through the blood circulation to various parts of the body, different tissues and different organs, and finally to the intracellular fluid, which is also mostly passive. The metabolism of drugs refers to the absorption of drugs in the body, and the distribution will be accompanied by changes in chemical structure, which also becomes biotransformation and mainly occurs in the liver. The excretion of drugs refers to the in vivo process of metabolism of drugs affecting the absorption and distribution of drugs, metabolism out of the body, and the organs of excretion are kidney, liver, gastrointestinal tract, etc.