CYP1A2 Isoenzyme Metabolism

Approximately 15% of all drugs used today are metabolized by the CYP1A2 isozyme. It is generally believed that there is no genetic polymorphism involved with this isozyme. Common drugs that are substrates for the CYP1A2 isozyme include
R-warfarin, theophylline, caffeine, and some benzodiazepines, antidepressants and antipsychotics. Although few in number, these drugs are commonly involved with a large number of clinically significant DIs. The most significant inhibitors of CYP1A2 include selected fluoroquinolones and fluvoxamine. Smoke (polycyclic aromatic hydrocarbons from cigarettes and charbroiled food), omeprazole, phenobarbital, phenytoin. rifampin and ritonavir are inducers of CYP1A2. Cruciferous vegetables (e.g., broccoli, cauliflower) can also induce this enzyme. Other drugs involved with CYP1A2 are listed in Table 3.

Table 3
Cytochrome P450 1A2 Enzyme
Substrates    Inducers Inhibitors
Acetaminophen Imipramine Charbroiled food Cimetidine
Amitriptyline Lidocaine Cigarette smoke Ciprofloxacin
Caffeine Methadone Omeprazole Clarithromycin
Chlorzoxazone Ondansetron Phenobarbital Enoxacin
Clarithromycin Phenacetin Phenytoin Erythromycin
Clomipramine Procarbazine Rifampin Fluvoxamine
Clozapine Propafenone Ritonavir Grapefruit juice
Cyclobenzaprine Prostaglandins    Isoniazid
Dantrolene R-warfarin    Ketoconazole
Desipramine Ritonavir    Levofloxacin
Diazepam Tacrine    Nalidixic acid
Diethylstilbestrol Tamoxifen    Norfloxacin
Estradiol Theophylline    Omeprazole
Flutamide Verapamil    Paroxetine
Fluvoxamine Warfarin (Risomer)       
Haloperidol Zileuton       

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