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- ACRONYMS AND DEFINITIONS
- CYP - Cytochrome P450
- Sensitive substrate - a drug whose exposure has been shown to be significantly altered by CYP2C19 inducers and/or inhibitors in studies. For other substrates, the clinical significance of inducer/inhibitor interactions is not as well-defined.
- NOT A COMPLETE LIST
- The information presented here is NOT A COMPLETE LIST of CYP2C19 inducers, inhibitors, and substrates
- Not all drug interactions are clinically significant. Potential drug interactions should be researched, and medication changes should only be made after consulting a health professional.
- CYTOCHROME P450
- Drug metabolism
- Cytochrome P450 (often abbreviated "CYP") is a class of liver enzymes involved in the metabolism of many medications. CYP enzymes are divided into subtypes (e.g. 2D6, 3A4, 2C8) based on their structure.
- Drugs may be metabolized by one or several different CYP enzymes. In some cases, one CYP enzyme is responsible for a majority of the drug's metabolism (major pathway), while other CYP enzymes contribute a small amount (minor pathway). Some drugs undergo no CYP metabolism, and some require CYP metabolism to become active. For example, clopidogrel (Plavix) has no antiplatelet effect until it is converted to its active metabolite by CYP2C19.
- CYP drug interactions
- Inducers and Inhibitors
- Inducers - CYP inducers increase enzyme activity and may decrease exposure to substrates
- Inhibitors - CYP inhibitors reduce enzyme activity and may increase exposure to substrates
- Certain chemicals and foods (e.g. tobacco smoke, grapefruit juice) may also act as CYP inducers and inhibitors
- One drug may inhibit or induce multiple enzymes and transporters (e.g. p-glycoprotein, OAT)
- Drugs may inhibit or induce the same enzyme they are metabolized by
- Inducers and inhibitors can be subdivided into strong, moderate, or weak depending on the degree of their effect
- Competitive inhibition
- If two drugs are metabolized by the same CYP enzyme, they may "compete" for the enzyme, and this can alter the metabolism of one or both of the drugs
- Genetic factors
- Genetic differences in the genes that code for CYP enzymes can lead to variations in their activity. Patients with alleles that increase enzyme activity are referred to as "rapid metabolizers," and those with suppressive alleles are called "poor metabolizers." People in the middle are called "intermediate" or "normal" metabolizers.
- CYP2C19 POOR METABOLIZERS
- Overview
- The genes that code for the CYP2C19 enzyme can vary between ethnicities and individuals. Some alleles decrease enzyme activity (loss-of-function alleles), while others increase activity (gain-of-function alleles).
- The most common CYP2C19 loss-of-function alleles are the *2 and *3 variants. One loss-of-function allele leads to a 47% reduction in CYP2C19 activity, and two loss-of-function alleles lead to a 65% reduction. People with one loss-of-function allele are considered "intermediate metabolizers," and people with two loss-of-function alleles are considered "poor metabolizers." [12]
- CYP2C19 metabolizer status is particularly important because the widely prescribed antiplatelet agent clopidogrel (Plavix®) must be metabolized by CYP2C19 to become active (see clopidogrel and CYP2C19 poor metabolizers)
- The prevalence of CYP2C19 alleles among different races is given below
- Prevalence of at least one loss-of-function allele by ethnicity (intermediate metabolizers)
- Asians 51 - 55%
- African-Americans 33 - 40%
- Caucasians 24 - 30%
- Mexican-Americans 18% [12]
- Prevalence of two loss-of-function alleles by ethnicity (poor metabolizers)
- Chinese 14%
- African-Americans 4%
- Caucasians 2% [13]
- IMPORTANT POINTS ABOUT DRUG INTERACTIONS
- Drug interactions are challenging
- Information on drug interactions can be difficult to assimilate
- Certain drug interactions and metabolic pathways are well-defined while others are not
- Factors that can make drug interactions challenging
- New drugs
- During drug development, the FDA requires interaction testing with medications that are known to have significant effects on CYP enzymes and transporters. Obviously, there is no way to test a new drug with every medication available, meaning most drugs come to market with incomplete interaction profiles. After the medication is prescribed to a large number of people, other drug interactions are inevitably discovered.
- Research
- Drug research often occurs in a laboratory setting (in vitro) with animals and cell cultures. Findings from these experiments do not always reflect what happens in the human body (in vivo).
- Evolving information
- Drug metabolism is an evolving field, and researchers are just beginning to understand all the different ways the body eliminates medications. Cytochrome P450 enzymes have been studied for a while, but cell transport systems (e.g. p-glycoprotein, OAT) are a relatively new area of pharmacology, and their role in drug elimination has not been completely elucidated.
- Important points
- Not all drug interactions are known or can be predicted
- Good information on possible drug interactions may not be available
- Not all drug interactions are clinically significant, and patients should consult their healthcare provider if they are concerned about a possible interaction
- Drug interaction checkers provide the most efficient and practical way to check for interactions among multiple medications. A free interaction checker is available from Drugs.com (see Drugs.com interactions checker).
- CYP2C19 INDUCERS
- CYP2C19 strong inducers
- Rifampin [1]
- CYP2C19 moderate inducers
- Enzalutamide (Xtandi®) [4]
- CYP2C19 inducers (class not well-defined)
- Tocilizumab (Actemra®) - indirect induction through inflammation suppression [6]
- Letermovir (Prevymis®) [4]
- Tumor Necrosis Factor inhibitors - indirect induction through inflammation suppression - (adalimumab, Humira®, certolizumab, Cimzia®, etanercept, Enbrel®, golimumab, Simponi®, infliximab, Remicade®) [6]
- St. John's Wort (Hypericum perforatum) [10,11]
- CYP2C19 INHIBITORS
- CYP2C19 strong inhibitors
- Amitriptyline (Elavil®) [9]
- Clomipramine (Anafranil®) [9]
- Fluconazole (Diflucan®) [1]
- Fluvoxamine (Luvox®) [1]
- Imipramine (Tofranil®) [9]
- Ticlopidine (Ticlid®) [1]
- CYP2C19 moderate inhibitors
- Eslicarbazepine (Aptiom®) [4]
- Esomeprazole (Nexium®) [1]
- Fluoxetine (Prozac®) [1]
- Moclobemide [1]
- Omeprazole (Prilosec®) [1]
- Voriconazole (Vfend®) [1]
- CYP2C19 weak inhibitors
- Allicin (garlic derivative) [1]
- Armodafinil (Nuvigil®) [1]
- Carbamazepine (Tegretol®) [1]
- Cimetidine (Tagamet®) [1]
- Desipramine (Norpramin®) [9]
- Etravirine (Intelence®) [1]
- Ethinyl estradiol [1]
- Felbamate [1]
- Fenofibrate (Tricor®, etc) [4]
- Fenofibric acid (Trilipix®) [4]
- Human growth hormone (HGH) [1]
- Ketoconazole (Nizoral®) [1]
- Nortriptyline (Pamelor®) [9]
- Oral contraceptives [1]
- Topiramate (Topamax®) [4]
- CYP2C19 inhibitors (class not well-defined)
- Cannabidiol (Epidiolex®) [4]
- Cenobamate (Xcopri™) [4]
- Lansoprazole (Prevacid®) [7]
- Nicardipine (Cardene®) [4]
- Oxcarbazepine (Trileptal®) [4]
- Telmisartan (Micardis®) [4]
- Vilazodone (Viibryd®) - in vitro studies only [4]
- CYP2C19 SUBSTRATES
- CYP2C19 sensitive substrates
- NOTE: A sensitive substrate is a drug whose exposure has been shown to be significantly altered by CYP2C19 inducers and/or inhibitors in studies
- Abrocitinib (Cibinqo®) [4]
- Cannabidiol (Epidiolex®) [4]
- Carisoprodol (Soma®) [4,7]
- Cilostazol (Pletal®) [4]
- Citalopram (Celexa®) [4]
- Clobazam (Onfi®) [4]
- Clopidogrel (Plavix®) [4]
- Dexlansoprazole (Dexilant®) [4]
- Diazepam (Valium®) [4,7]
- Esomeprazole (Nexium®) [4]
- Flibanserin (Addyi®) - minor substrate [4]
- Lansoprazole (Prevacid®) [1]
- Methadone [4]
- Omeprazole (Prilosec®) [1]
- Phenytoin (Dilantin®) [1]
- Tofacitinib (Xeljanz®) [4]
- CYP2C19 substrates
- NOTE: Compared to sensitive substrates, the clinical significance of inducer/inhibitor interactions with these drugs is not as well-defined
- Amitriptyline (Elavil®) [7]
- Apixaban (Eliquis®) [4]
- Arformoterol (Brovana®) [4]
- Brivaracetam (Briviact®) [4]
- Cenobamate (Xcopri™) [4]
- Chloramphenicol [2]
- Clomipramine (Anafranil®) [7]
- Cyclophosphamide [2]
- Doxazosin (Cardura®, Cardura XL®) [4, Cardura XL® PI]
- Fluoxetine (Prozac®) [7]
- Formoterol (Foradil®) [4]
- Imipramine (Tofranil®) [7]
- Indomethacin (Indocin®) [2]
- Lacosamide (Vimpat®) [4]
- Nelfinavir (Viracept®) [7]
- Nilutamide (Nilandron®) [2]
- Nortriptyline (Pamelor®) [7]
- Ospemifene (Osphena®) [4]
- Pantoprazole (Protonix®) [1]
- Prasugrel (Effient®) [4]
- Praziquantel (Biltricide®) [3]
- Primidone (Mysoline®) [2]
- Progesterone [2]
- Proguanil (Malarone®) [7]
- Propranolol (Inderal®) [4]
- Rabeprazole (Aciphex®) [7]
- Samidorphan (Lybalvi®) (minor substrate) [4]
- Sertraline (Zoloft®) [7]
- Suvorexant (Belsomra®) (minor substrate) [4]
- Teniposide [2]
- Terbinafine (Lamisil®) [4]
- Timolol (Timoptic®, Blocadren®) (minor substrate) [14]
- Voriconazole (Vfend®) [4]
- Warfarin (Coumadin®) [2]
- BIBLIOGRAPHY
- 1 - FDA drug development and drug interactions - CLICK HERE
- 2 - Flockhart DA. Drug Interactions: Cytochrome P450 Drug Interaction Table. Indiana University School of Medicine (2007). http://medicine.iupui.edu/clinpharm/ddis/table.aspx. Accessed [2011].
- 3 - SuperCYP website
- 4 - Manufacturer's Package Insert
- 5 - PubMed ID 11956508
- 6 - PubMed ID 11602509
- 7 - PubMed ID 12222994
- 8 - PubMed ID 21060077
- 9 - PubMed ID 17471183
- 10 - Carisoprodol PI
- 11 - PubMed ID 22606944
- 12 - PubMed ID 21060077
- 13 - Clopidogrel PI
- 14 - PMID 17461033 Timolol metabolism