Please note
- The information presented here is NOT A COMPLETE LIST of CYP2B6 inducers, inhibitors, and substrates
- An easy way to quickly search the drug lists is with your browser's Search/Find (Ctrl+F) tool
- 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.
- CYP - Cytochrome P450
- FDA - U.S. Food and Drug Administration
- Substrate - a drug that is metabolized by a certain enzyme is a substrate of that enzyme
- CYTOCHROME P450
- 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 (ex. 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
- Some drugs affect the action of CYP enzymes:
- Inducers - increase the
activity of CYP enzymes
- Inhibitors - block the action
of CYP enzymes
- When CYP inducers or inhibitors are taken with other medications that
are metabolized by the same enzyme, they can alter the metabolism of that
medication
- 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 and also inhibit or induce 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
- 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
- Compounding can also occur between CYP enzymes and cell transport
systems (ex. p-glycoprotein, OAT, etc.)
- 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"
- Gene variations in CYP enzymes can affect how an individual metabolizes
a drug
- 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 include the following:
- 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, or 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
- Interaction
- If Drug A is metabolized by CYP2B6, and it is taken with Drug B, a
CYP2B6 inducer, then blood levels of Drug A may be decreased
- Example:
- Drug A is metabolized by CYP2B6. Drug B is a CYP2B6 inducer.
- Drug A by itself = normal blood levels
- Drug A + Drug B = decreased levels of Drug A because Drug B has
increased CYP2B6 activity
CYP2B6 moderate inducers
- Efavirenz (Sustiva®) [1]
- Rifampin [1]
CYP2B6 weak inducers
- Nevirapine (Viramune®) [1]
CYP2B6 inducers (class uncertain)
- Phenobarbital [1]
- Ritonavir (Norvir®, Kaletra®) [6]
- 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]
- Interaction
- If a Drug A is metabolized by CYP2B6, and it is taken with Drug B, a
CYP2B6 inhibitor, then blood levels of Drug A may increase
- Example:
- Drug A is metabolized by CYP2B6. Drug B is a CYP2B6 inhibitor.
- Drug A by itself = normal blood levels
- Drug A + Drug B = increased blood levels of Drug A because Drug B has
inhibited CYP2B6
CYP2B6 weak inhibitors
- Clopidogrel (Plavix®) [1]
- Ticlopidine (Ticlid®) [1]
- Prasugrel (Effient®) [1]
- Interaction
- CYP2B6 substrates may be affected by CYP2B6 inducers and inhibitors (see
above)
- If two CYP2B6 substrates are taken together, they may compete for the
enzyme and the metabolism of one or both of the drugs may be affected
- Sensitive substrates are drugs that are known to be significantly
affected by CYP2B6 inhibitors and/or inducers
- Example:
- Drug A is metabolized by CYP2B6. Drug B is metabolized by CYP2B6.
- When Drug A is taken with Drug B they may compete for the CYP2B6
enzyme
- This competition may affect blood levels of either one or both of the
drugs
CYP2B6 sensitive substrates
- NOTE: These drugs are known to be
significantly affected by CYP2B6 inhibitors/inducers
- Efavirenz (Sustiva®) [1]
- Bupropion (Wellbutrin®) [1]
- Velpatasvir (Epclusa®) [6]
CYP2B6 substrates
- Cyclophosphamide (Procytox®) [1]
- Clopidogrel (Plavix®) [6]
- Diazepam (Valium®) [5]
- Ifosfamide (Ifex®) [3]
- Isotretinoin (Accutane®, Claravis®, etc.) (in vitro evidence only)
[6]
- Ketamine (Ketalar®) [3]
- Meperidine (Demerol®) [1]
- Methadone [3, 4]
- Mexiletine [5]
- Midazolam (Versed®) [5]
- Nevirapine (Viramune®) [5]
- Nicotine [3]
- Phenobarbital [3]
- Prasugrel (Effient®) [6]
- Procainamide [5]
- Propofol (Diprivan®) [3]
- Selegiline (Eldepryl®) [5]
- Tamoxifen [3,5]
- Temazepam (Restoril®) [5]
- Testosterone (Androgel®) [3]
- Valproic Acid (Depakote®) [5]
- BIBLIOGRAPHY
- What is PMID?
- PI = Manufacturer's Package Insert
- # PMID
- 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 - PMID 17073575
- 4 - PMID 18292673
- 5 - PMID 18781911
- 6 - Manufacturer's package insert
