Washington, DC — Behavioral therapies remain the first line of treatment for patients with overactive bladder, but high discontinuation rates with traditional second-line anticholinergic therapies suggest more treatment options are needed.

Among 29,369 women with overactive bladder who participated in a UK study, about 60% of OAB anticholinergic treatment regimens were discontinued at 6 months, 77% were discontinued at one year and 92% were discontinued at 3 years, Gopal et al reported in Obstetrics and Gynecology.

Extended-release formulations of the beta-3 adrenergic receptor agonist mirabegron (Myrbetriq, Astellas Pharmaceuticals) have demonstrated safety and effectiveness as a second-line OAB treatment and represent a viable alternative to anticholinergics, according to research presented at the American Academy of Physician Assistants IMPACT 2013 Product Theater.

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The FDA approved mirabegron for OAB in June 2012 based on findings from three phase-3 clinical trials involving nearly 5,000 patients. Mean patient age was 59 years, 94% were white and 72% were female. Patients included in the study had OAB symptoms for at least three months, with symptoms consisting of eight micturitions per day and at least three episodes of urgency with or without incontinence during a three-day period.

Data indicate daily 25 mg mirabegron is effective within eight weeks for reducing the number of daily incontinence episodes and micturitions. The recommended starting dose is 25 mg daily with or without food, but may be increased to 50 mg per day based on patient tolerability data.

The most commonly reported adverse reactions for mirabegron 25 mg and 50 mg were hypertension (11.7% and 7.5%, respectively, vs. 7.6% with placebo), nasopharyngitis (3.5% and 3.9% vs. 2.5%), urinary tract infection (4.2% and 2.9% vs. 1.8%) and headache (2.1% and 3.2% vs. 3%).

The FDA recommends periodic BP monitoring for those prescribed mirabegron, especially among patients with hypertension, as the medication is known to increase BP.  It is contraindicated in patients with systolic BP of 180mm Hg and/or diastolic BP of 110 mm Hg or more.

Because mirabegron is a moderate CYP2D6 inhibitor, patients taking CYP2DC substrates metoprolol and desipramine, or medications such as thioridazine, flecainide and propafenone that are metabolized by CYP2D6 should be monitored and have dosage adjusted accordingly.

Clinicians should also be cautious when administering mirabegron to patients with bladder outlet obstruction, the FDA advises.