The risk and severity of developing symptomatic palpitations when prescribed mirabegron for overactive bladder

Mirabegron is a new selective β3-adrenoreceptor agonist licensed for the treatment of overactive bladder (OAB). In clinical trials, mirabegron is well-tolerated with a low side-effect profile. There is little data available on the risks in a non-selected population. The presence of β-adrenoreceptors in cardiac and vascular tissue leads to the possibility of the development of adverse cardiovascular events. We conducted a consecutive cohort study to assess the risk of developing palpitations, the severity of the condition and to investigate any underlying risk factors that predispose patients with OAB to develop palpitations whilst taking mirabegron.

A consecutive cohort of patients with OAB was studied between February 2013 and June 2014. Patients were prescribed mirabegron 50mg daily and outcomes assessed at 6 weeks. Patients with known cardiac arrhythmias were excluded. In patients who developed palpitations, a detailed account of their symptoms and medical history were documented and a 12-lead electrocardiogram (ECG) was performed to assess heart rate, QT interval and the presence of any persisting arrhythmia was conducted.

A total of 279 patients were started on mirabegron. Eight patients (2.9%) reported palpitations whilst taking the drug. Two patients with a history of palpitations with no history of prolonged QT interval or arrhythmia on ECG developed worsening palpitations. The QTc was prolonged in two patients at 0.458 and 0.441s (QTc <420). Three patients developed chest pain or tightness. The palpitations resolved once therapy was stopped and did not result in serious adverse events such as hospitalisation.

Palpitations in an unselected population have a similar incidence to that demonstrated in previous drug trials. Palpitations may be associated with a worsening of cardiovascular dysfunction.