THE CYTOCHROME P-450 ENZYME SYSTEM

The term CYTOCHROME P-450 refers to a group of enzymes with are located on the endoplasmic reticulum. These enzymes are of particular importance when studying drug biotransformation and drug metabolism.

It is know that the gene for cytochrome P-450 has existed for more then 3.5 billion years. This indicates drug metabolism by the P-450 system is a new and secondary role for these enzyme systems.

The primary role for the P450 system seems to be one of metabolism and detoxification of endogenous compounds after they have been taken in by mouth in the process of eating. This accounts for the high concentrations of these enzymes located in the liver and small intestine.

The P-450 system can be altered by a number of mechanisms including inhibition and induction and can vary from person to person.
There are over 30 human P-450 isoenzyme systems that have been identified to date. The major ones responsible for drug metabolism are the CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2D6, CYP2E1, CYP3A4 and the CYP3A5-7.

Knowledge of the P-450 system is critical in understanding drug metabolism and drug interactions. Listed below are 3 links that will show 3 different tables: The first table shows what cytochrome system is involved in the metabolism of various drugs (substrates). The second table shows various drugs and the various cytochrome P-450 enzyme systems that either inhibit or induce that drugs metabolism. Lastly the third table shows the various cytochrome P-450 enzyme systems and shows what drugs induce or inhibit the various enzyme systems.

Table 1 - Various Drugs and the P-450 Systems Responsible for Their Metabolism

Table 2 - Various Drugs and the Variuos P-450 Enzymes that Inhibit or Induce their Metabolism

Table 3 - Various P-450 systems and What Drugs Inhibit or Induce the Enzyme System

Table 4 - Drugs / Foods that Induce or Inhibit Various Cytochrome P-450 Systems and the Drugs that are effected by this Induction or Inhibition.


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