What are the considerations for using Myrbetriq (mirabegron) and tamsulosin together in the management of urinary symptoms?

Mirabegron and Tamsulosin Combination Therapy for Urinary Symptoms

Mirabegron add-on therapy to tamsulosin is effective and safe for men with persistent overactive bladder symptoms who have inadequate response to tamsulosin monotherapy for lower urinary tract symptoms. 1, 2

Efficacy of Combination Therapy

• Combination therapy with mirabegron and tamsulosin demonstrates superior efficacy compared to tamsulosin monotherapy in reducing overactive bladder symptoms in men with lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH) 1, 2
• The combination results in significant improvements in:
  • Total Overactive Bladder Symptom Score (OABSS) 3
  • Urinary urgency and frequency 2
  • International Prostate Symptom Score (IPSS) storage symptom subscore 2
  • Quality of life indices 2
• The 2023 European Association of Urology guidelines specifically recommend combination treatment of an α1-blocker with mirabegron in patients with persistent storage LUTS after treatment with α1-blocker monotherapy 1

Safety Considerations

Cardiovascular Safety

• No clinically relevant cardiovascular interactions have been observed when adding mirabegron to established tamsulosin therapy or vice versa 4
• Combination therapy causes no statistically significant changes in pulse rate or systolic blood pressure compared to monotherapy 4
• Small decreases in diastolic blood pressure (2-4 mmHg) may occur but are generally not accompanied by orthostatic symptoms 4, 5
• Cardiovascular-related adverse events are uncommon with the combination therapy 5

Urinary Retention Risk

• The risk of urinary retention with mirabegron add-on therapy is low, with studies showing only 1-2 patients requiring catheterization in clinical trials 3, 6
• Post-void residual volume changes are not clinically meaningful when mirabegron is added to tamsulosin therapy 6
• The European Association of Urology guidelines do not recommend combination therapy in men with a post-void residual volume >150 mL 1

Pharmacokinetic Interactions

• Mirabegron increases tamsulosin Cmax by approximately 59% and AUC by 61% 7, 4
• Tamsulosin may slightly reduce mirabegron Cmax to 85% and AUC to 84% 4
• Despite these pharmacokinetic interactions, they do not translate to clinically significant safety concerns 7, 4

Clinical Application

• Consider mirabegron add-on therapy for men with persistent storage symptoms (urgency, frequency, nocturia) despite adequate treatment with tamsulosin 1, 2
• Start with tamsulosin monotherapy and add mirabegron if storage symptoms persist 3
• The standard dosing is:
  • Tamsulosin 0.4 mg daily
  • Mirabegron 25 mg daily initially, with potential increase to 50 mg daily after 4 weeks if needed 6, 2
• Monitor post-void residual volume, especially in men with elevated baseline values 1
• Assess for improvement in both voiding and storage symptoms after initiating combination therapy 2

Special Considerations

• Combination therapy is particularly beneficial for men with moderate-to-severe storage LUTS 1
• The safety profile of mirabegron add-on therapy appears favorable compared to antimuscarinic add-on therapy, with lower risk of dry mouth, constipation, and cognitive effects 2
• For elderly patients, monitor pulse rate changes, although studies show these remain within normal range 5
• The combination therapy has demonstrated efficacy and safety in both Japanese and Korean populations, suggesting broad applicability 2, 5