Tamoxifen with Rifampin Interaction Details
Brand Names Associated with Tamoxifen
- Nolvadex®
- Soltamox®
- Tamoxifen
Brand Names Associated with Rifampin
- Rifadin®
- Rifamate® (as a combination product containing Isoniazid, Rifampin)
- Rifampin
- Rifater® (as a combination product containing Isoniazid, Pyrazinamide, Rifampin)
- Rimactane®
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Dec 18, 2023
Interaction Effect
Reduced tamoxifen exposure
Interaction Summary
Avoid coadministration of tamoxifen with strong CYP3A4 inducers. In a pharmacokinetic study with rifampin (strong CYP3A4 inducer), tamoxifen AUC was reduced by 86% and Cmax reduced by 55%.
Severity
Major
Onset
Delayed
Evidence
Theoretical
How To Manage Interaction
Avoid concurrent use of tamoxifen with strong CYP3A4 inducers. Tamoxifen is extensively metabolized by CYP450 enzymes, including CYP3A4 in the formation of the metabolite N-desmethyl tamoxifen. Coadministration of rifampin and tamoxifen in a pharmacokinetic study significantly reduced tamoxifen exposure.
Mechanism Of Interaction
Induction of CYP3A4-mediated tamoxifen metabolism
Literature Reports
A) Plasma concentrations of tamoxifen and its active metabolite, endoxifen, were reduced by 24% and 66%, respectively, to subtherapeutic levels of 171.18 nanomoles/L (nM) and 15.75 nM 2-weeks post-rifampin therapy in a 38-year-old woman with a history of breast cancer and ulcerative colitis. The patient initiated adjuvant tamoxifen 20 mg/day and was closely monitored at a personalized tamoxifen clinic; she had therapeutic levels of tamoxifen and endoxifen at 4- and 10-month follow-up appointments. Due to an ulcerative colitis flare the following year, the patient initiated therapy with an anti-tumor necrosis factor alpha monoclonal antibody and subsequent rifampin 600 mg daily for latent tuberculosis. Upon initiation of rifampin, tamoxifen and endoxifen levels were within therapeutic range at 225.25 nM and 46.06 nM, respectively. Rifampin therapy was not well tolerated and discontinued after 10 days. Measured plasma concentrations of tamoxifen and endoxifen returned to within the therapeutic range 10-weeks post rifampin therapy .
Tamoxifen Overview
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Tamoxifen is used to treat breast cancer that has spread to other parts of the body in men and women. It is used to treat early breast cancer in women who have already been treated with surgery, radiation, and/or chemotherapy. It is used to reduce the risk of developing a more serious type of breast cancer in women who have had ductal carcinoma in situ (DCIS; a type of breast cancer that does not spread outside of the milk duct where it forms) and who have been treated with surgery and radiation. It is used to reduce the risk of breast cancer in women who are at high risk for the disease due to their age, personal medical history, and family medical history.
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Tamoxifen is in a class of medications known as antiestrogens. It blocks the activity of estrogen (a female hormone) in the breast. This may stop the growth of some breast tumors that need estrogen to grow.
Rifampin Overview
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Rifampin is used with other medications to treat tuberculosis (TB; a serious infection that affects the lungs and sometimes other parts of the body). Rifampin is also used to treat some people who have Neisseria meningitidis (a type of bacteria that can cause a serious infection called meningitis) infections in their noses or throats. These people have not developed symptoms of the disease, and this treatment is used to prevent them from infecting other people. Rifampin should not be used to treat people who have developed symptoms of meningitis. Rifampin is in a class of medications called antimycobacterials. It works by killing the bacteria that cause infection.
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Antibiotics such as rifampin will not work for colds, flu, or other viral infections. Using antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.
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Definitions
Severity Categories
Contraindicated
These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.
Major
This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.
Moderate
This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.
Minor
While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.
Onset
Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.
Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.
Evidence
Level of documentation of the interaction.
Established: The interaction is documented and substantiated in peer-reviewed medical literature.
Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.
How To Manage The Interaction
Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.
It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.
Mechanism Of Interaction
The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.
Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.
Where Does Our Information Come From?
Information for our drug interactions is compiled from several drug compendia, including:
The prescribing information for each drug, as published on DailyMED, is also used.
Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.
The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.