Relugolix and Saquinavir: 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
Saquinavir
No brand names on recordRelugolix
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.
Both of these medicines can affect your heart's rhythm. Saquinavir (an HIV medicine, usually boosted with ritonavir) and relugolix (Orgovyx, used for prostate cancer) can each stretch out a part of your heartbeat called the QT interval. When two drugs do this at the same time, the effect can add up and, in rare cases, lead to a dangerous irregular heartbeat.
Because of this, using these two together is generally not recommended. The good news is your care team knows how to handle this. Please don't stop or change either medicine on your own. Talk with your doctor or pharmacist so they can review your options and keep an eye on your heart if both are truly needed.
Effect: Additive QT-interval prolongation with concurrent ritonavir-boosted saquinavir and relugolix. Neither is a prodrug here; this is a pharmacodynamic (additive) interaction, not activation-dependent.
Severity/evidence: Labeled contraindicated; supporting data are theoretical (additive QT risk). Onset unspecified.
- Boosted saquinavir is contraindicated with QT-prolonging agents and with CYP3A4 substrates prone to life-threatening toxicity at elevated levels.
- If coadministration is unavoidable: obtain baseline ECG; do not initiate if QTc >450 msec.
- Repeat ECG after 3 to 4 days; discontinue one or both agents if QTc >480 msec or rises >20 msec from baseline.
- Correct electrolytes (K+, Mg2+) and review other QT-prolonging drugs.
What happens
An increased risk of QT interval prolongation
Interaction Deep Dive
This drug and ritonavir-boosted saquinavir each lengthen the QT interval. Ritonavir-boosted saquinavir must not be given together with CYP3A4 substrates in which elevated plasma levels could trigger life-threatening reactions, with agents that prolong the QT interval, or with agents that simultaneously raise saquinavir plasma concentrations and prolong the QT interval. When combined use of ritonavir-boosted saquinavir with a QT-prolonging agent cannot be avoided, obtain a baseline ECG. Coadministration should not be started when the QT interval is above 450 msec. Repeat an ECG during treatment following 3 to 4 days of concurrent therapy; stop one or both agents if the QT interval rises above 480 msec or increases by more than 20 msec relative to baseline1.
Why it happens (mechanism)
Additive QT interval prolongation
How to manage this interaction
Keep taking both medicines as prescribed until you've spoken with your care team. This combination is labeled contraindicated, so your prescriber will decide whether both are truly needed or whether an alternative fits better.
If both must be used together, your team will typically manage it by:
- Checking a baseline ECG before starting, and not starting if your QT reading is already high.
- Rechecking an ECG after about 3 to 4 days of using them together.
- Adjusting or stopping one medicine if the QT reading climbs too far.
Tell your pharmacist or doctor about any dizziness, fainting, or a fluttering or pounding heartbeat right away.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Relugolix and Saquinavir together?
Combining ritonavir-boosted saquinavir with relugolix is contraindicated because both prolong the QT interval and the effect can add up. Do not change either medicine yourself; talk with your doctor or pharmacist so they can choose the safest option and monitor your heart with ECGs if both are needed. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Relugolix and Saquinavir interaction?
It is rated contraindicated. These should generally not be used together.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Relugolix and Saquinavir interaction managed?
Keep taking both medicines as prescribed until you've spoken with your care team. This combination is labeled contraindicated, so your prescriber will decide whether both are truly needed or whether an alternative fits better. If both must be used together, your team will typically manage it by: Checking a baseline ECG before starting, and not starting if your QT reading is already high. Recheckin… 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 Relugolix or Saquinavir 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 (1)
- Product Information: INVIRASE(R) oral capsules, oral tablets, saquinavir mesylate oral capsules, oral tablets. Genentech Inc (per FDA), South San Francisco, CA, 2019. DailyMed
Keep reading about Saquinavir
Keep reading about Relugolix
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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