Lapatinib and Relugolix: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Lapatinib
Relugolix
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
If you take lapatinib (Tykerb) for cancer along with relugolix (Orgovyx), it's worth knowing about this pairing. Lapatinib can block a protein pump that normally helps push relugolix out of your body. When that pump is slowed, more relugolix can build up, which may raise the chance of side effects.
On top of that, both drugs can affect your heart's rhythm (something called QT prolongation). Together, that effect can add up. The good news is your care team can manage this by timing your doses, checking your blood minerals, and doing an ECG (heart tracing) when needed. Please don't stop or change either medicine on your own. Talk with your doctor or pharmacist first.
Effect: Increased relugolix exposure plus additive QT prolongation.
Mechanism: Lapatinib inhibits P-glycoprotein (P-gp); relugolix is a P-gp substrate, so efflux is reduced and relugolix AUC/Cmax rise. Both agents independently prolong QT, giving additive PD risk. Evidence is theoretical; severity rated major.
- Avoid concurrent use where possible.
- If unavoidable: give relugolix first, separate doses by at least 6 hours, monitor for adverse reactions.
- Relugolix may be interrupted up to 2 weeks for short P-gp inhibitor courses; if held greater than 7 days, restart with 360 mg loading dose then 120 mg daily.
- Correct electrolytes; consider periodic ECG and electrolyte monitoring, especially with long QT syndrome, CHF, or electrolyte abnormalities.
What happens
Increased relugolix exposure and an increased risk of QT interval prolongation
Interaction Deep Dive
Because relugolix is a P-gp substrate, it should not be taken together with P-gp inhibitors, since doing so can raise relugolix exposure and thereby heighten the likelihood of adverse reactions. When the two cannot be avoided, give the relugolix-containing product first, keep the two doses at least 6 hours apart, and increase the frequency of monitoring for adverse reactions12. For a brief course of a P-gp inhibitor, relugolix therapy can be paused for as long as 2 weeks, then resumed once the P-gp inhibitor has been stopped. Should the relugolix interruption exceed 7 days, reinitiate therapy using a 360 mg loading dose on day one, followed by 120 mg once daily thereafter1. When relugolix is given alongside medications that prolong the QT interval, the effects on the QT interval may be additive. In individuals with congenital long QT syndrome, congestive heart failure, or recurrent electrolyte disturbances, as well as those receiving drugs recognized to prolong the QT interval, weigh whether the advantages of androgen deprivation therapy such as relugolix justify the possible risks. Electrolyte abnormalities should be corrected, and periodic ECG and electrolyte monitoring should be considered1.
Why it happens (mechanism)
Inhibition of P-gp-mediated efflux transport of relugolix; additive QT interval prolongation
How to manage this interaction
Keep taking both medicines as prescribed unless your care team tells you otherwise. Here is how teams typically handle this combination:
- They may try to avoid using both together when another option exists.
- If both are needed, they may have you take relugolix first and separate the two doses by at least 6 hours.
- They may watch you more closely for side effects and check your heart rhythm (ECG) and blood minerals like potassium and magnesium.
- In some cases relugolix may be paused briefly during a short course of lapatinib, with the dose individualized by your team when restarting.
Ask your pharmacist or prescriber about dose timing and any heart or lab monitoring you may need.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) When relugolix (a P-gp substrate) was given together with erythromycin (a P-gp and CYP3A inhibitor), the AUC and Cmax of relugolix rose by 3.5-fold and 2.9-fold, respectively 1.
Common questions
Can I take Lapatinib and Relugolix together?
Lapatinib can raise relugolix levels and both can affect heart rhythm, so use them together only under close medical supervision. Do not change either medicine on your own; ask your care team about dose timing, spacing doses by at least 6 hours, and heart and electrolyte monitoring. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Lapatinib and Relugolix interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Lapatinib and Relugolix interaction managed?
Keep taking both medicines as prescribed unless your care team tells you otherwise. Here is how teams typically handle this combination: They may try to avoid using both together when another option exists. If both are needed, they may have you take relugolix first and separate the two doses by at least 6 hours. They may watch you more closely for side effects and check your heart rhythm (ECG) and… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Lapatinib or Relugolix need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (2)
- Product Information: ORGOVYX oral tablets, relugolix oral tablets. Sumitomo Pharma America, Inc (per FDA), Marlborough, MA, 2025. DailyMed
- Product Information: MYFEMBREE(R) oral tablets, relugolix, estradiol, norethindrone acetate oral tablets. Myovant Sciences Inc (per FDA), Brisbane, CA, 2021. DailyMed
Keep reading about Lapatinib
Keep reading about Relugolix
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