What is the comparison between Myrbetriq (mirabegron) and Ditropan (oxybutynin) for treating overactive bladder?

Mirabegron vs. Oxybutynin for Overactive Bladder

Mirabegron (Myrbetriq) is generally preferred over oxybutynin (Ditropan) for treating overactive bladder due to its superior tolerability profile and similar efficacy, particularly in older adults and those concerned about cognitive side effects. 1, 2

Mechanism of Action

• Mirabegron is a β3-adrenoceptor agonist that relaxes the detrusor muscle during the storage phase, increasing bladder capacity 3
• Oxybutynin is an antimuscarinic agent that blocks acetylcholine receptors, reducing involuntary detrusor contractions 1

Efficacy Comparison

• Both medications demonstrate similar efficacy in reducing overactive bladder symptoms:
  • Reduced frequency of micturition episodes per 24 hours 4, 1
  • Decreased urgency episodes 4, 1
  • Reduced incontinence episodes 5, 1
  • Increased voided volume per micturition 4, 1

Side Effect Profile

• Mirabegron advantages:

  • Significantly lower incidence of dry mouth (2.1% vs 8.6% for antimuscarinics) 2, 1
  • No increase in cognitive impairment risk 6
  • Lower discontinuation rates due to better tolerability 2, 6
  • Minimal anticholinergic burden 6

• Oxybutynin disadvantages:

  • Higher rates of dry mouth, constipation, and blurred vision 1
  • Increased risk of cognitive impairment, especially in elderly patients 6
  • Higher discontinuation rates due to side effects 1, 6

Special Populations

Elderly Patients

• Mirabegron is particularly advantageous in patients ≥65 years:

  • Demonstrated safety and efficacy in this population 5
  • Lower risk of cognitive side effects 6
  • Starting dose of 25mg is recommended with option to increase to 50mg 5

• Oxybutynin should be used with extreme caution in elderly patients due to:

  • Increased risk of anticholinergic side effects 1
  • Higher potential for cognitive impairment 6

Patients with Bladder Outlet Obstruction

• Mirabegron has been studied specifically in males with lower urinary tract symptoms and bladder outlet obstruction with favorable safety profile 3
• Antimuscarinics like oxybutynin should be used with extreme caution in patients with bladder outlet obstruction due to risk of urinary retention 1, 4

Treatment Algorithm

1. First-line therapy: Behavioral therapies (bladder training, pelvic floor exercises, fluid management) 1

2. Second-line therapy:

   • For most patients, especially elderly or those concerned about cognitive effects: Mirabegron 25mg daily, titrating to 50mg if needed 5, 6
   • For younger patients without cognitive concerns and with lower cost considerations: Oxybutynin (with awareness of higher side effect profile) 1, 6

3. For inadequate response to monotherapy: Consider combination therapy with mirabegron plus an antimuscarinic 1

Cost Considerations

• Oxybutynin is generally less expensive than mirabegron 6
• However, cost-effectiveness analyses suggest mirabegron may be more cost-effective when considering:
  • Lower discontinuation rates 6
  • Fewer anticholinergic side effects 6
  • Reduced healthcare utilization related to adverse events 6

Common Pitfalls and Caveats

• Avoid oxybutynin in patients with:

  • Narrow-angle glaucoma 1
  • History of urinary retention 1
  • Impaired gastric emptying 1
  • Cognitive impairment or risk factors for dementia 6

• Monitor blood pressure with mirabegron, although cardiovascular safety profile is generally favorable 2, 5

• Transdermal oxybutynin may be considered if oral antimuscarinic side effects are problematic but still carries risk of systemic effects 1