Drug metabolism refers to the chemical change process of drugs in the body. Most drugs lose their activity after being metabolized, and are converted into extremely high water-soluble metabolites, which are beneficial to excretion from the body. There are also some drugs that are hardly metabolized in the body and are excreted as original drugs. For more details, please read Factors Affecting Pharmacokinetics of Drugs.
The metabolism of drugs requires the participation of enzymes. The liver is an important organ for drug metabolism. The cytochrome P-450 enzyme system of liver microsomes is the main enzyme system that promotes drug metabolism, so it is called liver drug enzymes. Some drugs can also be decomposed by related enzymes in other tissues.
The availability and content of liver drug enzymes are not unstable, and individual differences are large, and they are easily affected by certain drugs. Any drug that can enhance the activity of liver drug enzymes or accelerate the synthesis is called drug enzyme inducer, which can accelerate the metabolism of the drug itself and some other drugs, which is one of the reasons for drug tolerance. For example, phenobarbital has a strong drug-enzyme induction effect, and continuous medication can accelerate its own metabolism and that of the anticoagulant warfarin, reducing its efficacy. Any drug that can reduce the activity or synthesis of drug enzymes is called drug enzyme preparations, which can slow down the metabolism of some other drugs and enhance the drug effect. For example, chloramphenicol is a drug enzyme inhibitor, which can slow down the metabolism of phenytoin sodium. Taking the two drugs together can increase the blood concentration of phenytoin sodium, enhance the efficacy, and even cause toxic reactions. Therefore, it is necessary to pay attention to the mutual influence of the drugs when combining drugs.
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