Amitriptyline and Iobenguane I 131: 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
Iobenguane I 131
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.
Here's what's going on. Iobenguane I-131 (Azedra) is a special radioactive treatment that works by getting taken up into certain cells, much like your body's own adrenaline-type chemicals. Amitriptyline (Elavil) blocks that same uptake pathway. So if you take amitriptyline around the time of your Azedra treatment, it can keep the Azedra from getting where it needs to go.
This can throw off the dose calculations and make the treatment work less well. The good news is this is very manageable. Your care team plans the timing carefully, and they will tell you exactly when to pause and restart amitriptyline. Never stop it on your own, just talk with your doctor or pharmacist.
Mechanism: Amitriptyline inhibits catecholamine (norepinephrine) reuptake transporters, the same uptake mechanism iobenguane I-131 uses to enter tumor cells. Competitive interference reduces iobenguane uptake.
Effect / direction: Reduced iobenguane uptake leads to inaccurate dosimetry and reduced therapeutic efficacy. Onset rapid; evidence is theoretical but clinically important given the treatment's purpose.
- Management: Discontinue amitriptyline at least 5 half-lives before dosimetry and before each therapeutic dose.
- Wait at least 7 days after each iobenguane I-131 dose before restarting.
- Coordinate all timing with the treating nuclear medicine/oncology team; antidepressant taper should be physician-supervised.
What happens
Inaccurate dosimetry calculations or reduced efficacy
Interaction Deep Dive
Agents that lower catecholamine reuptake or empty catecholamine stores, tricyclic antidepressants among them, can hinder the cellular uptake of iobenguane, which may compromise dosimetry calculations or the effectiveness of iobenguane I-131. These medications should be stopped for a minimum of 5 half-lives prior to giving either the dosimetry dose or a therapeutic dose of iobenguane I-131, and the interfering agent(s) should not be resumed until at least 7 days have passed following each iobenguane I-131 dose1.
Why it happens (mechanism)
Interference with iobenguane uptake into cells
How to manage this interaction
The main tool here is timing. Because amitriptyline can block Azedra from entering cells, your care team will plan a washout so the treatment can work and the dose can be calculated correctly.
- Your team will typically have you stop amitriptyline well before the dosimetry scan and each treatment dose (about 5 half-lives ahead).
- They usually have you wait at least 7 days after each dose before restarting it.
- Because stopping an antidepressant abruptly can cause withdrawal, this should be planned and supervised by your prescriber.
Keep taking both exactly as directed, and ask your oncology team and pharmacist to confirm the exact stop-and-restart schedule for you.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Amitriptyline and Iobenguane I 131 together?
Amitriptyline can block Azedra from entering cells, hurting its accuracy and effectiveness, so your care team will schedule when to pause and restart it. Do not stop either drug on your own; coordinate the timing with your doctor and pharmacist. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Amitriptyline and Iobenguane I 131 interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How is the Amitriptyline and Iobenguane I 131 interaction managed?
The main tool here is timing. Because amitriptyline can block Azedra from entering cells, your care team will plan a washout so the treatment can work and the dose can be calculated correctly. Your team will typically have you stop amitriptyline well before the dosimetry scan and each treatment dose (about 5 half-lives ahead). They usually have you wait at least 7 days after each dose before resta… 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 Iobenguane I 131 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: AZEDRA(R) intravenous injection, iobenguane I 131 intravenous injection. Progenics Pharmaceuticals Inc (per FDA), New York, NY, 2018.
Keep reading about Amitriptyline
Keep reading about Iobenguane I 131
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