Mirabegron XR Drug Interactions: What to Avoid and What to Tell Your Doctor

Before starting Mirabegron XR (Myrbetriq), it is essential that you and your doctor review all of your current medications — including prescriptions, over-the-counter drugs, vitamins, and supplements. Mirabegron XR has several clinically important drug interactions, primarily because it inhibits a liver enzyme called CYP2D6. This guide covers the most important interactions and what to do about them.

Why Mirabegron XR Can Affect Other Medications: CYP2D6 Inhibition

Mirabegron XR is a moderate inhibitor of the cytochrome P450 enzyme CYP2D6. This enzyme is produced in the liver and is responsible for breaking down many common medications. When CYP2D6 is inhibited, drugs that are normally metabolized by it stay in the body longer and can build up to higher levels than expected, potentially intensifying their effects or causing toxicity.

This is not unique to Mirabegron XR — many medications inhibit CYP2D6 — but it is important to be aware of if you take any drugs from the list below.

Major Drug Interactions with Mirabegron XR

1. Digoxin (Lanoxin) — Monitor Closely

Digoxin is a heart medication used for atrial fibrillation and heart failure. It has a very narrow therapeutic index, meaning the difference between a therapeutic dose and a toxic dose is small. When Mirabegron XR is added to digoxin therapy, it can increase digoxin levels by approximately 10-14%.

What to do: If you take digoxin, tell your prescriber before starting Mirabegron XR. Start with the lowest digoxin dose. Your doctor will monitor your serum digoxin concentration and adjust your digoxin dose as needed.

2. CYP2D6-Metabolized Drugs — Increased Drug Levels

Many commonly prescribed drugs are metabolized by CYP2D6. When mirabegron inhibits this enzyme, these drugs may have higher than expected blood levels. The most clinically important ones include:

Beta-blockers (metoprolol, carvedilol, propranolol): Levels may increase, potentially causing slower heart rate, low blood pressure, or dizziness. Monitor closely.

Antiarrhythmics (flecainide, propafenone): Increased levels of narrow therapeutic index antiarrhythmics can cause serious cardiac effects. Dose adjustment may be needed.

Tricyclic antidepressants (amitriptyline, imipramine, desipramine): Elevated TCA levels may intensify anticholinergic effects, sedation, and cardiac risk.

Opioids (codeine, tramadol): Codeine and tramadol are prodrugs converted by CYP2D6 to their active forms. Mirabegron's inhibition of CYP2D6 may reduce this conversion, potentially decreasing pain relief.

Antipsychotics (haloperidol, risperidone, thioridazine): Levels may increase, raising the risk of side effects including QT prolongation.

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3. Warfarin (Coumadin) — Monitor INR

Warfarin is a blood thinner with a narrow therapeutic index. While mirabegron did not show a significant pharmacokinetic interaction with warfarin in a single-dose study, the effect of mirabegron on multiple doses of warfarin and on warfarin pharmacodynamic endpoints (INR) has not been fully characterized. If you take warfarin, continue regular INR monitoring when starting or changing your mirabegron dose.

4. Antimuscarinic OAB Drugs — Risk of Urinary Retention

Mirabegron XR is sometimes prescribed in combination with solifenacin (Vesicare) — this combination is actually FDA-approved. However, combining mirabegron with other antimuscarinic OAB medications (oxybutynin, tolterodine, darifenacin) increases the risk of urinary retention, especially in patients with bladder outlet obstruction. Monitor carefully if combination therapy is used.

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5. Medications That Affect Mirabegron Levels

Some drugs can change how much mirabegron XR your body absorbs or processes:

Ketoconazole (antifungal): Strong CYP3A inhibitor and P-glycoprotein inhibitor. Can increase mirabegron levels. Use with caution; dose adjustments may be considered.

Rifampin (antibiotic): A potent inducer of liver enzymes that can significantly reduce mirabegron blood levels, potentially reducing its effectiveness.

What to Tell Your Doctor Before Starting Mirabegron XR

Before starting Mirabegron XR, tell your prescriber about:

All heart medications, including digoxin, beta-blockers, and antiarrhythmics

Blood thinners including warfarin

Antidepressants, especially tricyclics (amitriptyline, imipramine) and some SSRIs

Antipsychotics or mood stabilizers

Any antifungal medications (especially ketoconazole or itraconazole)

Any antibiotics, especially rifampin

Any other OAB medications you take or have recently taken

High blood pressure and any blood pressure medications

For more foundational information about Mirabegron XR — including how it works, what it treats, and standard dosing — see our complete guide to what is Mirabegron XR.