What are the differences between oxybutynin (antimuscarinic) and mirabegron (beta-3 adrenergic agonist) for treating Lower Urinary Tract Symptoms (LUTS)?

From the Guidelines

Mirabegron is generally preferred over oxybutynin for treating Lower Urinary Tract Symptoms (LUTS) due to its better side effect profile, particularly in elderly patients or those concerned about cognitive effects, as evidenced by a meta-analysis of eight randomized controlled trials 1. The primary difference between oxybutynin and mirabegron lies in their mechanisms of action and side effect profiles. Oxybutynin, an antimuscarinic agent, blocks muscarinic receptors in the bladder, reducing involuntary detrusor muscle contractions, whereas mirabegron, a beta-3 adrenergic agonist, activates beta-3 receptors in the bladder to promote relaxation during the storage phase. Some key points to consider when choosing between oxybutynin and mirabegron include:

• Oxybutynin typically starts at 5mg twice daily or 5-10mg once daily for extended-release formulations, but commonly causes anticholinergic side effects including dry mouth, constipation, blurred vision, cognitive impairment, and is contraindicated in narrow-angle glaucoma.
• Mirabegron has a standard dose of 25-50mg once daily, with dose reduction needed in severe renal or hepatic impairment, and generally has fewer anticholinergic side effects but may cause hypertension, headache, and nasopharyngitis.
• Mirabegron is well tolerated in the elderly and in patients with multiple comorbidities, but is contraindicated in patients with severe uncontrolled hypertension 1.
• Both medications take 2-4 weeks for full effect, and patients should be monitored for efficacy and side effects, with combination therapy considered under medical supervision in cases of inadequate response. It is essential to weigh the benefits and risks of each medication, considering the individual patient's medical history, comorbidities, and concerns, to make an informed decision about the most suitable treatment option, as supported by the 2023 European Association of Urology guidelines on the management of non-neurogenic male lower urinary tract symptoms 1.

From the Research

Differences between Oxybutynin and Mirabegron for LUTS

• Mechanism of Action: Oxybutynin is an antimuscarinic agent, whereas mirabegron is a beta-3 adrenergic agonist 2.
• Efficacy: Both oxybutynin and mirabegron have been shown to be effective in relieving LUTS symptoms, including urinary incontinence, urgency, and frequency 3, 4.
• Side Effects: Oxybutynin is associated with anticholinergic side effects, such as dry mouth, constipation, and blurred vision, whereas mirabegron has a better safety profile with fewer side effects 2, 4.
• Comparison with Other Treatments: Mirabegron has been compared to tolterodine, another antimuscarinic agent, and has been shown to have a similar efficacy with a better safety profile 4.
• Specific Patient Populations: Mirabegron has been studied in patients with neurogenic lower urinary tract dysfunction and has been shown to be effective and safe in this population 5.
• Symptom Relief: Both oxybutynin and mirabegron have been shown to relieve ureteral stent-related symptoms, including pain and lower urinary tract discomfort 3.
• Dosing and Administration: Oxybutynin is typically dosed at 5 mg/day, while mirabegron is dosed at 50 mg/day 3.
• Long-term Effects: The long-term effects of oxybutynin and mirabegron on LUTS symptoms have not been extensively studied, but mirabegron has been shown to have a sustained efficacy over time 3, 4.