Myrbetriq (Mirabegron): A beta-3 adrenergic agonist indicated for the treatment of overactive bladder

On June 28, 2012, FDA approved the beta-3 adrenergic agonist mirabegron (Myrbetriq) for the treatment of OAB with symptoms of urge urinary incontinence, urgency, and urinary frequency. Mirabegron works by relaxing the detrusor smooth muscle during the storage phase of the urinary bladder fill-void cycle.

Efficacy. Mirabegron was evaluated in three, 12-week, double-blind, randomized, placebo-controlled, multicenter clinical trials of patients with overactive bladder and complaining of symptoms of urge urinary incontinence, urgency, and urinary frequency. Results showed that mirabegron 25 mg and 50 mg statistically significantly reduced the number of times a patient had an incontinence episode (adjusted mean difference from placebo; -0.41 for 50 mg in study 1, -0.34 for 25 mg in study 2, and -0.40 to -0.42 for 25 mg and 50 mg, respectively, in study 3) and the number of times a patient urinated (adjusted mean difference from placebo; -0.60 for 25 mg in study 1, -0.61 for 25 mg in study 2, and -0.47 to -0.42 for 25 mg and 50 mg, respectively, in study 3) during a 24-hour period.

Safety. The most common reported adverse reactions (occurring in >2% of subjects and more often than placebo) during the above-mentioned clinical trials of mirabegron were hypertension, nasopharyngitis, urinary tract infection, and headache. Mirabegron can increase blood pressure, and therefore, periodic blood pressure determinations are recommended (especially in hypertensive patients). Mirabegron is not recommended for use in severe uncontrolled hypertensive patients. A higher risk of urinary retention is present in patients suffering from bladder outlet obstruction or taking antimuscarinic drugs for overactive bladder. Caution should be used in the administration of mirabegron in these patients.