Cytochrome P450 Enzymes
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38 terms
Terms | Definitions |
|---|---|
 Cytochrome P450 Enzymes | Group of 50+ enzymes in the human body that are responsible for the metabolism of most drugs. 49 genes and 16 subunits have been identified. Designated by CYP number(1) letter number(2). |
| number (1) | designates the family of similar enzymes |
| letter | designates the subfamily of enzymes |
| number (2) | designates the specific enzyme expressed by a particular gene |
| First pass effect | the first encounter of a drug with these cytochrome P450 enzymes |
| first pass effect possible outcomes | 1. Drug is converted to a metabolite (becomes more soluble for excretion by the kidney) 2. Activation of a drug 3. Inhibition of the CYP enzyme |
| examples of drugs that are activated during first pass | Codeine (prodrug of morphine) Losartan/Cozaar Acetaminophen/Tylenol |
| Induction of enzyme production | Increased synthesis or the enzyme; decreased degradation of the enzyme |
| Some drugs are metabolized by more than one enzyme causing... | less toxicity to the liver (because it has 3-4 different pathways to use) and less drug-drug interactions (because 2 drugs won't be competing for the same enzyme as much) |
| Racemic mixture drugs | Drugs that contain both stereoisomers and usually require 2 different CYP enzymes for metabolism. They go through liver metabolism and elimination |
| Example of a racemic drug | Coumadin/Warfarin |
| R(+) isomer of Coumadin/Warfarin is metabolized by.. | CYP1A2 and CYP3A family of enzymes |
| S(-) isomer of Coumadin/Warfarin is metabolized by.. | only CYP2C9. It is 5x as potent as the R isomer |
| Drugs that inhibit enzymes | Quinidine and fluvastatin (Lescol) |
| Quinidine | inhibits CYP2D6 metabolized by CYP3A |
| Fluvastatin (Lescol) | inhibits CYP2C9 metabolized by CYP2C9 |
| Competitive inhibition | This does not usually inhibit the activity of an enzyme at therapeutic doses (ex: Nifiedipine/Procardia XL and Simvastatin/Zocor both use CYP3A but have no drug-drug interactions) |
| Enzyme polymorphism | Genes control enzymes. Some are enhanced in certain populations, while others are lacking in certain populations. |
| CYP2D6 enhanced in... | Ethiopian and Saudi Arabian populations. 2D6 is not inducible, and these levels are responses to the high amount of toxic alkaloids in their diet, causing there to be multiple causes of the gene. CYP2D6 chews up a variety of drugs. |
| Drugs rendered ineffective in Ethiopian and Saudi Arabian populations | Antidepressants, neuroleptics |
| Prodrugs extensively activated in Ethiopian and Saudi Arabian populations | Codeine (turned into vast amounts of morphine) |
| individuals lacking CYP2D6 | Predisposition to drug toxicity from antidepressant or neuroleptics. Codeine, tramadol/Ultram rendered ineffective due to lack of activation. |
| Patients lacking CYP2C9 | Ineffective in clearing (S)-warfarin/Coumadin. Be cautious with even 0.5 mg warfarin/day. |
| Patients lacking CYP2C19 | Higher cure rates for peptic ulcers treated with omeprazole/Prilosec due to sustained, high plasma levels achieved. |
| Percentages of people lacking CYP2C19 | 2-5% Caucasians 20% Asians |
| Percentages of people lacking CYP2D6 | 5-10% Caucasians 1-3% African Americans and Chinese |
| Percentage of drugs metabolized by CYP2D6 | 25% |
| Substance that inhibits CYP3A system in the small intestine | Grapefruit juice |
| CYP3A | family of four major enzymes (3,4,5,7) |
| Percentage of meds processed by CYP3A | 50% |
| Metoprolol/Lopressor | metabolized by CYP2D6 |
| Simvastatin/Zocor | metabolized by CYP3A |
| Erythromycin | metabolized by and inhibits CYP3A, causes nausea in many pts |
| Fluvastatin/Lescor | metabolized by and inhibits CYP2C9 |
| Medical marijuana/D9-THC | metabolized by CYP2C9 |
| Omeprazole/Prilosec | metabolized by CYP2C19 |
| Codeine | metabolized by CYP2D6 |
| Nifedipine/Procardia | metabolized by CYP3A |
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