Can Myrbetriq (mirabegron) cause fluid retention or edema?

Mirabegron (Myrbetriq) and Fluid Retention/Edema

Mirabegron (Myrbetriq) can cause fluid retention and peripheral edema, though it is less common than with other medication classes such as calcium channel blockers.

Mechanism and Risk Factors

Mirabegron is a β3-adrenoreceptor agonist approved for treating overactive bladder syndrome. Unlike alpha-blockers or calcium channel blockers that cause edema through direct vasodilatory effects, mirabegron's mechanism for causing fluid retention appears to be related to its effects on adipose tissue metabolism 1.

Key risk factors that may increase the likelihood of developing edema while on mirabegron include:

• Advanced age
• Pre-existing cardiovascular disease
• Concurrent use of other medications that cause fluid retention
• Renal insufficiency (particularly severe impairment) 2
• Hepatic impairment (particularly moderate impairment) 2
• Prolonged standing or sitting 3

Clinical Presentation

When mirabegron causes fluid retention, it typically presents as:

• Bilateral and symmetric peripheral edema
• Initially affecting ankles and lower legs, potentially extending upward
• May not be associated with other symptoms like dyspnea 3
• Can develop within the first few months of therapy

Monitoring Recommendations

For patients taking mirabegron:

• Monitor for weight gain and peripheral edema, particularly during the first few months of therapy
• Perform periodic assessment of lower extremities
• Instruct patients to report significant swelling promptly 3
• Consider baseline evaluation of cardiovascular status before initiating therapy in high-risk patients

Management Approach

If edema develops in a patient taking mirabegron:

1. Evaluate severity and impact on quality of life

   • Determine if the edema is affecting daily activities or causing discomfort

2. Non-pharmacological interventions:

   • Elevate legs when sitting or lying down
   • Use compression stockings if appropriate
   • Limit sodium intake

3. Medication adjustments:

   • Consider dose reduction if symptoms are mild
   • For persistent or severe edema, consider switching to an alternative medication for overactive bladder

4. Pharmacological management:

   • Low-dose diuretic therapy may be considered for persistent cases 3
   • Loop diuretics (e.g., furosemide) are often effective for medication-induced edema 4

5. Monitor for improvement:

   • Follow up to assess response to interventions
   • Continue to monitor for signs of worsening edema or development of heart failure symptoms

Special Considerations

• Patients with renal impairment: Mirabegron exposure increases with declining renal function (31%, 66%, and 118% higher in mild, moderate, and severe renal impairment, respectively) 2, potentially increasing the risk of fluid retention.

• Patients with hepatic impairment: Mirabegron exposure is 19% and 65% higher in mild and moderate hepatic impairment, respectively 2, which may increase the risk of adverse effects including edema.

• Patients with pre-existing cardiovascular disease: Exercise caution as fluid retention could potentially exacerbate underlying heart failure.

When to Discontinue Mirabegron

Consider discontinuation if:

• Severe or persistent edema despite interventions
• Development of symptoms suggestive of heart failure (dyspnea, orthopnea, etc.)
• Patient experiences significant discomfort or decline in quality of life due to edema

While mirabegron has shown promise in treating overactive bladder symptoms with potentially fewer side effects than anticholinergic medications 5, clinicians should remain vigilant about monitoring for fluid retention, especially in high-risk patients.