Cytochrome P450 (Cyp450) is an important enzyme that causes the breakdown of many important drugs and helps in elimination from the body. Some drugs when used can interact with this enzyme and thus inhibit or enhance its function. The result is an increased or decreased levels, respectively, of drugs metabolized by cyp450.
Which drugs are metabolized by Cytochrome P450?
There are many drugs which are metabolized by cyp450 but the most common and important ones are:
Statin
Warfarin
Selective Serotonin Reuptake Inhibitors (SSRIs) – sertraline, citalopram, fluoxetine
Theophylline
Phenytoin
Oral contraceptive pills (OCPs)
Codeine
Caffeine
The mnemonic we suggest for remembering these drugs is:
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What are enzyme inducers?
Inducers are those drugs that interact with and increase the activity of the cytochrome p450 (Cyp450) enzyme.
Increased activity of Cyp450 results in the increased metabolism of some drugs, and subsequently reduces their therapeutic concentration leading to therapeutic failure. For example, if inducers are taken alongside oral contraceptive pills (OCPs) by a woman, it will result in increased metabolism of OCPs and result in contraceptive failure.
Enzyme inducers include:
Anticonvulsants: phenytoin, carbamazepine, phenobarbitone
Glucocorticoids
Antimicrobials: rifampicin, griseofulvin
St John’s Wort: a herbal medicine used for depression
Nicotine, cigarette smoke
Alcohol
What are enzyme inhibitors?
In contrast to inducers, Inhibitors are those drugs that interact with and decrease the activity of the cytochrome p450 (Cyp450) enzyme.
This decreased cyp450 activity will naturally result in the decreased metabolism of the drugs, mentioned above (remember the Star Wars mnemonic). As a result, there is an accumulation of these in the body and thus increased levels. Some of these drugs in excessive levels, e.g., warfarin, theophylline, etc, will cause deleterious effects like fatal bleeding or arrhythmias.
Enzyme inhibitors include:
Azole antifungals: ketoconazole, fluconazole
Antibiotics: sulfonamides, metronidazole, ciprofloxacin, chloramphenicol, macrolides, and isoniazid
Cimetidine
Omeprazole
Sodium valproate
Grapefruit
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