Drug Metabolizing Enzymes
A number of enzymes may be involved in drug metabolism. In some case more than one enzyme may metabolize the same drug. The enzymes that metabolize the most drugs are members of the Cytochrome P-450 family. The enzymes are produced, and metabolism occurs, primarily in the liver. The different Cytochrome p-450 enzymes are abbreviated to CYP followed by an alphanumeric series that specifies which enzyme, and then which version of that enzyme.
In 2004, at the request of the Food and Drug Administration, AACC survey pharmacogenomics experts that subscribe to its listserv or attended certain meetings, to list what they considered the most important metabolizing enzymes. That “Top 10” list of enzymes, and some of the drugs each metabolizes follows:
| Enzyme | Examples of Drugs Metabolized | Typical Diseases or Conditions |
| 1. CYP 2D6 | Fuvoxamine, paroxetine, haloperidol | Antidepressants, Antiarrythmics, Neurological Diseases |
| 2. TPMT (Thiopurine methyltransferase) | Azathioprine, mercaptopurines | childhood leukemia, antirejection, autoimmune disease |
| 3. CYP 2C9 | Warfarin | Blood clotting disorders |
| 4. CYP 2C19 | Mephentoin, omeprazole | Epilepsy |
| 5. NAT (N-acetyl transferase) | Caffeine, isoniazid, sulfamethazine | Stimulant, tuberculosis, antibiotic |
| 6. CYP 3A5 | nifedipine, cyclosporine | Antihypertensive, antirejection |
| 7. UGT1A1 (UDP-Glucuonosyltransferase) | Oxazepam, estradiol | Antianxiety, birth control |
| 8. MDR-1 (Multidrug resistance gene 1) | Warfarin | Blood clotting disorders |
| 9. CYP 2B6 | Bupropion | Antidepressant |
| 10. DPD (dihydropyrimidine dehydrogenase) | 5-fluorouracil | Chemotherapeutic |