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30th August 2024
Cytochrome P450
Cytochrome p450 enzymes are found in the hepatocytes and they play an important role in drug metabolism. These enzymes are particularly involved in phase I reactions such as oxidation, reduction, and hydrolysis of ingested medications. Certain drugs are known as cytochrome p450 ‘inducers’ and inhibitors. Inducers increase the amount of the enzyme and speed up the oxidation or clearance of a drug. Inhibitors reduce the activity of the enzyme thereby increasing the plasma concentration of the drug being metabolised. This may lead to adverse effects.
| Inhibitors | Inducers |
|---|---|
| SSRIs: fluoxetine, sertraline
Anti-fungals: ketoconazole, fluconazole Isoniazid Cimetidine Omeprazole Sodium valproate Acute alcohol intake Antibiotics: ciprofloxacin, erythromycin |
St John’s Wort
Chronic alcohol intake Phenytoin Carbamazepine Rifampicin Smoking Grapefruit juice |
| Enzyme | Prevalence | Substrates | Inducers | Inhibitors | Role |
|---|---|---|---|---|---|
| CYP3A4 | Most abundant in liver and intestines | Statins, calcium channel blockers, benzodiazepines, immunosuppressants | Rifampicin, St. John’s wort, phenytoin | Grapefruit juice, diltiazem, macrolides, ketoconazole, ritonavir | Drug metabolism and detoxification |
| CYP2C9 | Significant portion in liver | Warfarin, phenytoin, NSAIDs | Rifampicin, barbiturates | Amiodarone, fluoxetine, fluconazole | Metabolism of therapeutic agents and endogenous compounds |
| CYP2D6 | Smaller percentage of hepatic CYPs, metabolises ~25% of all meds | Antidepressants, antipsychotics, beta-blockers, opioids | – | Quinidine, paroxetine | Personalised medicine, genetic variability |
| CYP1A2 | Predominantly in liver | Caffeine, theophylline, some antipsychotics | Polycyclic aromatic hydrocarbons, cruciferous vegetables | – | Metabolism of xenobiotics and endogenous substrates |
| CYP2E1 | Liver and other tissues | Ethanol, acetaminophen (toxic metabolite), some anaesthetics | Ethanol, isoniazid | Disulfiram | Metabolism of drugs and environmental toxins, oxidative stress, liver injury |
Reference
Gilani B, Cassagnol M. Biochemistry, Cytochrome P450. [Updated 2023 Apr 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557698/
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