Can you mix Mybetriq (mirabegron) and oxybutynin?

Combining Mirabegron (Mybetriq) and Oxybutynin for Overactive Bladder

Yes, mirabegron (Mybetriq) and oxybutynin can be safely combined for treating overactive bladder when monotherapy is insufficient, and this combination may provide improved efficacy compared to either medication alone. 1

Rationale for Combination Therapy

Combination therapy with these medications works through complementary mechanisms:

• Mirabegron: A β3-adrenergic receptor agonist that relaxes the detrusor muscle
• Oxybutynin: An antimuscarinic that blocks acetylcholine receptors to reduce bladder contractions

When patients have inadequate symptom control with a single agent, combination therapy may provide better outcomes:

• Combination therapy has been shown to improve efficacy outcomes over monotherapy 2
• The different mechanisms of action can address multiple aspects of bladder dysfunction

Evidence Supporting Combination Therapy

Research demonstrates several benefits of combination therapy:

• Studies show combination therapy can increase bladder capacity and reduce detrusor pressure 3, 4
• Combination therapy has shown effectiveness in treatment-resistant cases 3, 5
• In patients with neurogenic bladder who were refractory to oxybutynin alone, adding mirabegron significantly improved clinical and urodynamic parameters 4

Side Effect Considerations

The main consideration when combining these medications is the potential for additive side effects:

• Antimuscarinic side effects from oxybutynin include:

  • Dry mouth (71.4%)
  • Constipation (15.1%)
  • Blurred vision (9.6%)
  • Dizziness (16.6%) 1

• Mirabegron side effects are generally milder and include:

  • Hypertension
  • Nasopharyngitis
  • Urinary tract infections 2

• Combination therapy may increase:

  • Constipation compared to solifenacin alone
  • Dry mouth compared to mirabegron alone 2

Contraindications and Cautions

Exercise caution or avoid this combination in patients with:

• Narrow-angle glaucoma (absolute contraindication for antimuscarinic agents) 6, 1
• Impaired gastric emptying or history of urinary retention 6
• Significant bladder outlet obstruction
• Cognitive impairment (particularly with oxybutynin)

Monitoring Recommendations

When using this combination:

1. Monitor for urinary retention (consider checking post-void residual)
2. Assess for antimuscarinic side effects (dry mouth, constipation, blurred vision)
3. Monitor blood pressure (particularly with mirabegron)
4. Evaluate treatment efficacy through symptom assessment

Treatment Algorithm

1. First-line approach: Begin with behavioral therapies (bladder training, pelvic floor exercises, fluid management) 6

2. Second-line therapy: If behavioral approaches are insufficient, add a single agent:

   • Mirabegron may be preferred in older adults due to better cognitive safety profile 1
   • Oxybutynin is effective but has higher anticholinergic burden

3. Combination therapy: If monotherapy provides inadequate symptom control:

   • Add mirabegron to existing oxybutynin therapy
   • Consider starting with lower doses of each medication to minimize side effects
   • Titrate doses based on efficacy and tolerability

4. Treatment failure: If combination therapy fails, consider referral to a specialist for advanced options such as:

   • OnabotulinumtoxinA injections
   • Sacral neuromodulation
   • Peripheral tibial nerve stimulation 1

This approach provides a structured pathway for managing overactive bladder symptoms while minimizing adverse effects.