DESIGNATIONS FOR HEPATIC ISOFORMS ACTIVE IN DRUG METABOLISM ::
In its simplest form the isoform nomenclature system is nothing more than a series of laboratory code names for enzymes present in the liver or other places in the body and responsible for metabolism (oxidation dealkylation or hydroxylation ) of drugs and other foreign chemicals following the CYP code for cytochrome P450 the first number represents families of enzymes with more than 40% identity in amino acid sequence Subfamilies are designated by the letters in the next position and the individual enzyme is denoted by the final number
Moreover some drugs may be metabolized by more than one of the systems (that is the enzymes lack specificity for some substrates ) Thus even when one enzyme system may be induced or inhibited by an interacting drug the metabolism of a second drug may (or may not) proceed without substantial change Table 2 presents basic biochemical information about the better studied isoenzymes identified in human liver and extrahepatic tissues These isoform families are responsible for much of the drug metabolism observed in people here is a brief description of each family
Isoform organs Substrates Inhibitors Inducers
3A3-5 Liver and Nifedipine Ketoconazole Phenobarbital
extrahepatic erthromycin rifampicin
cyclosporine dexamethasone
cortisol
2C8-10 Liver Tolbutamine s- Sulfaphenazole Phenobarbital
warfarin phenytoin rifampicin
Phenacetin
1A2 Liver caffeine Furafylline Omeprazole
theophylline smoking
2C18 Liver Mephenytoin phenobarbital
rifampicin
2D6 Liver Dextrometh- Quinidine
orphan sparteine
debrisoquine
2A6 Liver Coumarin phenobarbital
rifampicin
2E1 Liver and Chloroxazone Tetrahydrofurane
extrahepatic
1A1 Extrahepatic Tetrahydrofurane Ethanol
isoniazide
diabetes
2B6 Liver
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