Amitriptyline and Lonafarnib: 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
Amitriptyline
Lonafarnib
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 amitriptyline (Elavil) and lonafarnib (Zokinvy) can affect the timing of your heartbeat. Doctors call this QT prolongation. When you take two medicines that do this together, the effect can add up and, in rare cases, lead to a dangerous irregular heart rhythm.
The good news is that your care team knows how to watch for this. They may check your heart with an ECG, keep an eye on things like your potassium and magnesium levels, and decide the safest plan for you. Please don't stop or change either medicine on your own. Just talk with your pharmacist or doctor so they can guide you.
Effect: Additive QTc prolongation with increased risk of torsade de pointes and other serious arrhythmias.
Mechanism: Both agents independently prolong the QT interval (pharmacodynamic additive effect). Neither is a prodrug relevant to this interaction; the concern is PD, not PK.
Evidence: Theoretical. Severity: Major. Onset: Unspecified.
Management:
- Avoid concomitant use where possible.
- If unavoidable, obtain baseline and periodic ECGs at initiation and during co-therapy.
- Correct electrolytes (K+, Mg2+) and review other QT-prolonging agents and bradycardia risk.
What happens
An increased risk of QT interval prolongation and torsade de pointes
Interaction Deep Dive
Do not use lonafarnib, an agent that prolongs the QTc interval, together with other medications that prolong the QTc interval, because doing so can cause a larger increase in the QTc interval along with adverse reactions linked to QTc prolongation, such as torsade de pointes, additional serious arrhythmias, and sudden death. When concurrent use is unavoidable, obtain ECGs at the start of and throughout the concomitant use1.
Why it happens (mechanism)
Additive QT interval prolongation
How to manage this interaction
Both medicines can lengthen the QT interval, so the safest approach is often to avoid using them together when an alternative exists. That is a decision for your prescriber, not something to change on your own.
If your team decides you need both:
- They may check your heart rhythm with ECGs when starting and during treatment.
- They may monitor and correct blood minerals like potassium and magnesium.
- Keep taking both exactly as prescribed unless told otherwise.
Tell your pharmacist or doctor about all your medicines, and report fainting, dizziness, or a fluttering heartbeat right away.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Amitriptyline and Lonafarnib together?
Taking amitriptyline and lonafarnib together can add up to prolong the QT interval and raise the risk of a dangerous heart rhythm; this pairing is best avoided, but if both are needed your team can manage it with ECG monitoring. Do not change either medicine on your own. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Amitriptyline and Lonafarnib 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 Amitriptyline and Lonafarnib interaction managed?
Both medicines can lengthen the QT interval, so the safest approach is often to avoid using them together when an alternative exists. That is a decision for your prescriber, not something to change on your own. If your team decides you need both: They may check your heart rhythm with ECGs when starting and during treatment. They may monitor and correct blood minerals like potassium and magnesium.… 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.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Amitriptyline or Lonafarnib 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: ZOKINVY(TM) oral capsules, lonafarnib oral capsules. Eiger BioPharmaceuticals Inc (per FDA), Palo Alto, CA, 2024. DailyMed
Keep reading about Amitriptyline
Keep reading about Lonafarnib
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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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