Foscarnet and Amitriptyline: 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
Foscarnet
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. Amitriptyline (Elavil), a tricyclic antidepressant, and foscarnet (Foscavir), an antiviral, can each stretch out the timing of your heartbeat (called the QT interval). When you take them together, that effect can add up and, in rare cases, lead to a dangerous irregular heartbeat.
I want you to know this concern is mostly based on how these drugs work rather than lots of reported cases, so try not to panic. Please don't stop either medicine on your own. Talk with your doctor or pharmacist. They can decide the safest plan for you, which may include watching your heart more closely or choosing a different option.
Additive QT prolongation with combined amitriptyline and foscarnet, raising the risk of torsades de pointes, ventricular arrhythmias, and cardiac arrest.
- Mechanism: pharmacodynamic (additive), not metabolic. Both agents independently prolong the QT interval. Neither is a prodrug here.
- Direction: additive cardiotoxicity, increased arrhythmia risk.
- Evidence: theoretical; severity rated major.
- Onset: unspecified.
- Management: concurrent use is not recommended. If unavoidable, obtain baseline/serial ECGs, correct electrolytes (K+, Mg2+), avoid other QT-prolonging agents, and consider alternatives.
What happens
An increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest)
Interaction Deep Dive
In certain patients, foscarnet has the potential to lengthen the QT interval, a change that can lead to ventricular tachycardia, ventricular fibrillation, and torsades de pointes. Since tricyclic antidepressants can likewise extend the QT interval and raise the likelihood of arrhythmias, giving foscarnet together with tricyclic antidepressants is advised against21.
Why it happens (mechanism)
Additive cardiac effects
How to manage this interaction
The safest approach on file is to avoid using these two together. Because both can prolong the QT interval, combining them is not recommended.
- Keep taking both exactly as prescribed until you speak with your care team. Do not stop either one on your own.
- Your prescriber may choose an alternative to one of these drugs, or if both are truly needed, monitor you more closely (such as with heart tracing and electrolyte checks).
- Tell your team right away if you feel fainting, dizziness, a racing or fluttering heartbeat, or palpitations.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Foscarnet and Amitriptyline together?
Amitriptyline and foscarnet can each prolong the QT interval, and together they raise the risk of a dangerous heart rhythm, so combining them is generally not recommended. Do not stop either drug yourself; ask your prescriber or pharmacist about a safer plan. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Foscarnet and Amitriptyline 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 Foscarnet and Amitriptyline interaction managed?
The safest approach on file is to avoid using these two together. Because both can prolong the QT interval, combining them is not recommended. Keep taking both exactly as prescribed until you speak with your care team. Do not stop either one on your own. Your prescriber may choose an alternative to one of these drugs, or if both are truly needed, monitor you more closely (such as with heart tracin… 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 Foscarnet or Amitriptyline 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)
Keep reading about Amitriptyline
Keep reading about Foscarnet
These medications also interact with supplements
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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