The absorption, distribution, metabolism and excretion of drugs in the body is a complex process. Different classes of drugs and different drug properties have their own different metabolic laws. CTX and MTX are absorbed quickly and completely and degraded within a short time when injected intravenously; 5-FU is affected by the first-pass effect and absorbed irregularly, and its efficacy varies greatly among individuals; cytarabine and menadione are destroyed in the digestive tract, so they are ineffective when taken orally. Anthracyclines are unstable in the digestive tract, and vincristine is poorly absorbed in the body, so they cannot be taken orally, but only injected. Most of the antitumor drugs disappear quickly after injection, and the blood concentration of some drugs can be reduced to very low within a few minutes, such as MMC, VCR, BLM, etc. The blood concentration can drop rapidly, and it is difficult to be measured after 30~60 minutes. HCPT, 6-MP, etc. have a half-life of a few hours, and are widely distributed in the body, and the concentration is higher in the tumor and liver and kidney, but the selectivity is poor. After drug injection, the rate of excretion in the body varies with different drugs, for example, many different metabolites can be measured in a short time after nitrogen mustard injection, MTX and 5-FU are excreted from urine faster, VCR, VLB and actinomycin-D can be measured in bile soon after injection, and most of them are excreted from feces.