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- Please note
- The information presented here is NOT A COMPLETE LIST of CYP2D6 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.
- ACRONYMS AND DEFINITIONS
- CYP - Cytochrome P450
- Substrate - a drug that is metabolized by a certain enzyme is a substrate of that enzyme
- CYTOCHROME P450
- Overview
- Cytochrome P450 (often abbreviated "CYP") is a class of enzymes that is involved in the metabolism of many medications
- Cytochrome P450 enzymes are located primarily in the liver
- Cytochrome P450 enzymes are subdivided into classes (e.g. 2D6, 3A4, 2C8, etc.) based on their structure
- Drug metabolism
- Drugs may be metabolized by one subclass of CYP enzyme (ex. 3A only), or they may be metabolized by a number of CYP enzymes (ex. 2C8, 3A4, and 2C19)
- In some cases, one CYP enzyme may be responsible for the majority of the drug's metabolism while other CYP enzymes contribute a nonsignificant amount of metabolism
- Some drugs undergo no CYP metabolism
- CYP drug interactions
- Inducers and Inhibitors
- Inducers - CYP inducers increase the activity of CYP enzymes. This may increase the metabolism of other drugs that are substrates of the enzyme reducing their exposure.
- Inhibitors - CYP inhibitors reduce the activity of CYP enzymes. This may decrease the metabolism of other drugs that are substrates of the enzyme increasing their exposure.
- Certain chemicals and foods (ex. tobacco smoke and grapefruit juice) may also act as CYP inducers and inhibitors
- Drugs may be metabolized by a CYP enzyme while also inhibiting or inducing the enzyme at the same time
- Inducers and inhibitors can be subdivided into strong, moderate, or weak based on how much of an effect they have on the enzyme
- 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
- Compounded interactions
- When a person is taking three or more drugs, the potential for compounded interactions exists
- Compounding can also occur between CYP enzymes and cell transport systems (ex. p-glycoprotein, OAT, etc.)
- Example:
- Drug A is metabolized by CYP2D6 and CYP2C9
- Drug B inhibits CYP2D6. Drug C inhibits CYP2C9
- When Drug A is taken with Drug B, its elimination is partially decreased, but it is not significant
- When Drug A is taken with Drug B and Drug C, its elimination is decreased substantially and the interaction becomes significant
- Genetic factors
- Different genes code for each CYP enzyme
- Since individuals vary in their genetic makeup, their CYP genes may also vary
- Some people have genes that produce CYP enzymes that are less effective. These people are often referred to as "poor metabolizers."
- Some people have genes that produce CYP enzymes that are more effective. These people are often referred to as "rapid metabolizers." Rapid metabolizers may experience toxicity with some medications (see rapid metabolizers below)
- Gene variations in CYP enzymes can affect how an individual metabolizes a drug
- RAPID METABOLIZERS AND OPIOIDS
- Overview
- CYP2D6 metabolizes codeine to morphine, its active form. Likewise, dihydrocodeine is metabolized by CYP2D6 to dihydromorphine. Tramadol is metabolized by CYP2D6 to an active metabolite (M1) that has more potent opioid activity than the parent compound.
- Patients who are CYP2D6 rapid metabolizers may experience opioid toxicity (e.g. respiratory depression) when given codeine, dihydrocodeine, or tramadol because they achieve quick and high levels of the active compound. Conversely, poor metabolizers may not receive adequate analgesia.
- Respiratory depression and death have occurred in children who received codeine after surgery. These children were often found to be ultra-rapid CYP2D6 metabolizers. Because of this unforeseeable risk, codeine, dihydrocodeine, and tramadol are contraindicated in children under twelve.
- Prevalence of ultra-rapid CYP2D6 metabolizers by ethnicity
- North Africans, Ethiopians, and Arabs 16 - 28%
- African-Americans 3%
- Caucasians 1 - 10%
- Chinese and Japanese 0.5 - 1%
- Hispanics 0.5 - 1% [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-documented while many are not
- Factors that can make drug interactions challenging
- New drugs
- When a new drug is being developed, the FDA requires that it be tested for drug interactions with a small number of medications that are known to have significant interactions
- Obviously, there is no way to test a medication in every possible drug combination that may occur. This means most drugs come to market with incomplete drug interaction profiles.
- After a medication is prescribed to a large number of people, other drug interactions are inevitably discovered
- Research
- Much of the research involving drug metabolism and drug interactions occurs in vitro meaning in a lab, or outside of the human body
- Animal models and cell cultures are often used to test drugs for metabolic pathways and interactions
- Findings from in vitro experiments do not always translate into what actually happens in the human body (in vivo)
- Evolving information
- Drug metabolism is an evolving field of medicine and pharmacology
- Researchers are just beginning to understand all the different systems that are involved in how the body metabolizes and eliminates drugs
- Cell transport systems (ex. p-glycoprotein, OAT, etc.) are a relatively new area of pharmacology and information about how these systems affect drug elimination is evolving
- 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 significant
- Always consult your physician or pharmacist before changing your medication if you are concerned about a possible drug interaction
- CYP2D6 INDUCERS
- CYP2D6 inducers (class not well-defined)
- Tocilizumab (Actemra®) - indirect induction through inflammation suppression [6]
- Tumor Necrosis Factor inhibitors - indirect induction through inflammation suppression - (adalimumab, Humira®, certolizumab, Cimzia®, etanercept, Enbrel®, golimumab, Simponi®, infliximab, Remicade®) [6]
- CYP2D6 INHIBITORS
- CYP2D6 strong inhibitors
- Bupropion (Wellbutrin®) [1]
- Fluoxetine (Prozac®) [1]
- Metoclopramide (Reglan®) [8]
- Paroxetine (Paxil®) [1]
- Quinidine [1]
- CYP2D6 moderate inhibitors
- Cinacalcet (Sensipar®) [1]
- Dronedarone (Multaq®) [6]
- Duloxetine (Cymbalta®) [1]
- Mirabegron (Myrbetriq®) [6]
- Terbinafine (Lamisil®) [1]
- CYP2D6 weak inhibitors
- Amiodarone (Cordarone®) [1]
- Amphetamines (in vitro evidence) [6]
- Asenapine (Saphris®) [6]
- Celecoxib (Celebrex®) [1,6]
- Cimetidine (Tagamet®) [1]
- Desipramine (Norpramin®) [11]
- Desvenlafaxine (Pristiq®) [1]
- Diltiazem (Cardizem®) [1]
- Diphenhydramine (Benadryl®) [1]
- Echinacea [1]
- Escitalopram (Lexapro®) [1]
- Febuxostat (Uloric®) [1,6]
- Gefitinib (Iressa®) [1]
- Hydralazine (Apresoline®) [1]
- Hydroxychloroquine (Plaquenil®) [1]
- Imatinib (Gleevec®) [1]
- Imipramine (Tofranil®) [11]
- Methadone [1]
- Nortriptyline (Pamelor®) [11]
- Oral contraceptive pills [1]
- Propafenone (Rythmol®) [1]
- Ranitidine (Zantac®) [1]
- Ritonavir (Norvir®) [1]
- Sertraline (Zoloft®) [1]
- Telithromycin (Ketek®) [1]
- Venlafaxine (Effexor®) [6]
- Viloxazine (Qelbree®) [6]
- Verapamil (Calan®, Isoptin®, etc.) [1]
- CYP2D6 inhibitors (class not well-defined)
- Amitriptyline (Elavil®) [3]
- Chlorpheniramine (Chlor-Trimeton®) [7]
- Chlorpromazine (Thorazine®) [8]
- Citalopram (Celexa®) [8]
- Clobazam (Onfi®) [6]
- Clomipramine (Anafranil®) [2]
- Cobicistat (part of Stribild®) [6]
- Doxepin [2,9]
- Fluphenazine [8]
- Fluvoxamine (Luvox®) [8]
- Haloperidol (Haldol®) [8]
- Hydroxychloroquine (Plaquenil®) (possible, not well-defined) [12]
- Hydroxyzine (Vistaril®) [2,10]
- Lorcaserin (Belviq®) [6]
- Niacin (Niaspan®, Slo-Niacin®) [5]
- Nicardipine (Cardene®) [6]
- Peginterferon alfa-2b (PegIntron®) [6]
- Perphenazine [8]
- Sertraline (Zoloft®) [8]
- Thioridazine (Mellaril®) [8]
- Ticlopidine (Ticlid®) [2, 8]
- Vilazodone (Viibryd®) - in vitro studies only [6]
- CYP2D6 SUBSTRATES
- CYP2D6 sensitive substrates
- NOTE: These drugs are known to be significantly affected by CYP2D6 inhibitors and inducers
- Amphetamines (Adderall®, Vyvanse®, etc.) [6]
- Aripiprazole (Abilify®) [6]
- Atomoxetine (Strattera®) [1,6]
- Brexpiprazole (Rexulti®) [6]
- Codeine (see CYP2D6 rapid metabolizers) [8]
- Desipramine (Norpramin®) [1]
- Dextromethorphan (Robitussin DM®, etc.) [1]
- Dihydrocodeine (Trezix®) - see CYP2D6 rapid metabolizers [6]
- Iloperidone (Fanapt®) [6]
- Methadone [6]
- Metoprolol (Toprol®) [1]
- Nebivolol (Bystolic®) [1]
- Perphenazine [1]
- Pitolisant (Wakix®) [6]
- Propafenone (Rythmol®) [6, 8]
- Risperidone (Risperdal®) [6, 8]
- Timolol (Timoptic®, Blocadren®) [6]
- Tolterodine (Detrol®) [1]
- Tramadol (Ultram®) - see CYP2D6 rapid metabolizers [6,8]
- Venlafaxine (Effexor®) [1]
- Viloxazine (Qelbree®) (major substrate) [6]
- Vortioxetine (Trintellix®) [6]
- Thioridazine (Mellaril®) - has a narrow therapeutic window [8]
- CYP2D6 substrates
- Amitriptyline (Elavil®) [8]
- Arformoterol (Brovana®) [6]
- Benzhydrocodone (Apadaz®) [6]
- Cariprazine (Vraylar®) (minor substrate) [6]
- Carvedilol (Coreg®) [6]
- Chlorpheniramine (Chlor-Trimeton®) [8]
- Chlorpromazine (Thorazine®) [8]
- Ciclesonide (Alvesco®, Omnaris®) [6]
- Clomipramine (Anafranil®) [8]
- Clonidine (Catapres®) [4]
- Clozapine (Clozaril®) [8]
- Donepezil (Aricept®) [8]
- Doxazosin (Cardura®, Cardura XL®) [6, Cardura XL® PI]
- Doxepin [8]
- Duloxetine (Cymbalta®) [8]
- Flecainide (Tambocor®) [6]
- Fluoxetine (Prozac®) [8]
- Fluphenazine [8]
- Fluvoxamine (Luvox®) [8]
- Formoterol (Foradil®) [6]
- Haloperidol (Haldol®) [8]
- Ibrutinib (Imbruvica®) - minor substrate [6]
- Imipramine (Tofranil®) [8]
- Ivermectin (Stromectol®) - in vitro only - minor substrate [6]
- Letermovir (Prevymis®) [6]
- Metaxalone (Skelaxin®) [6]
- Metoclopramide (Reglan®) [8]
- Mirtazapine (Remeron®) [6]
- Mexiletine [6]
- Nicardipine (Cardene®) [6]
- Nortriptyline (Pamelor®) [8]
- Olanzapine (Zyprexa®) (minor substrate) [6]
- Ondansetron (Zofran®) [8]
- Oxycodone (Oxycontin®, Percocet®) (minor substrate) [2,6]
- Paliperidone (Invega®) (minor substrate)[6]
- Paroxetine (Paxil®) [8]
- Promethazine (Phenergan®) [8]
- Propranolol (Inderal®) [6]
- Tamoxifen [2,8]
- Tamsulosin (Flomax®) [6]
- Tiotropium (Spiriva®) (minor substrate) [6]
- Trimipramine (Surmontil®) [8]
- Umeclidinium (Anoro Ellipta®) [6]
- 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 - PMID 20570945
- 5 - PMID 15081432
- 6 - Manufacturer's package insert (for drug listed)
- 7 - PMID 11936702
- 8 - PMID 19601803
- 9 - PMID 15520506
- 10 - PMID 9616188
- 11 - PMID 17471183
- 12 - PMID 10848718
- 13 - Codeine sulfate PI