mirabegron (BETMIGA⁰). Poorly effective in urge urinary incontinence

Mirabegron interacts with many other drugs via cytochrome P450 isoenzymes. It also has additive adverse effects, in particular cardiac disorders, when combined with antimuscarinic drugs. In view of animal data and the lack of clinical data, mirabegron should not be used by women who are or may be pregnant. In practice, drugs have little value in treating urinary urgency attributed to "overactive bladder". The risk of adverse drug reactions is rarely justified, even when the disorder is severe. Antimuscarinic disorders, such as dry mouth, are less frequent with mirabegron than with antimuscarinic drugs. Like antimuscarinic drugs, mirabegron can cause cardiac arrhythmias, especially tachycardia. Mirabegron may also cause a dose-dependent increase in blood pressure. Other adverse effects include rare cases of kidney stones and rare but sometimes serious skin reactions. When a treatable cause of urinary urgency with incontinence has been ruled out and non-drug measures have failed, recourse to an antimuscarinic drug is slightly effective but exposes patients to numerous, potentially severe adverse effects. Mirabegron (Betmiga⁰, Astellas Pharma), a beta-3 adrenergic receptor agonist, is authorised for use in this setting in the European Union. Clinical evaluation of mirabegron is mainly based on five randomised, double-blind trials versus antimuscarinic drugs, lasting 3 to 12 months and including about 8000 patients with urinary urgency. Mirabegron and the antimuscarinic comparators were similarly effective, even after antimuscarinic drug failure. A meta-analysis of four placebo-controlled trials including about 3500 patients suggested that mirabegron was poorly effective: on average, treatment prevented one episode of urinary incontinence every 2 days.