Overactive bladder (OAB) symptoms in the older population are rarely defined as a singular cause, given age related changes and existing co-morbidities such as cognitive and functional impairment (1). Antimuscarinic agents have been the mainstay of oral therapy for OAB symptoms; however, they are associated with suboptimal efficacy and anticholinergic burden, which is especially concerning in older, frail person, which can affect tolerability (1-3). Mirabegron is not funded by the Pharmaceutical Benefits Scheme in Australia and therefore affordability plays a vital role in initiation and compliance to therapy. The prescription of mirabegron is made available in our continence clinic through a hospital subsidy. The aim of this study is to describe our clinical experience in an outpatient clinic setting on the efficacy and tolerability of mirabegron as a treatment option in management of OAB symptoms in the older person.

This was a retrospective review of electronic medical records of patients aged more than 65 years old who were prescribed mirabegron for OAB symptoms between 1st January 2016 and 31st August 2018 at the aged care Continence Clinic. Electronic medical records were individually reviewed for demographic data, relevant medical history (including cognitive impairment), previous pharmacotherapy for OAB symptoms and reasons for discontinuation, urinary symptoms of OAB reported, available 3 day bladder diary to monitor treatment response during follow up at 4 weeks and 3 months, pre and post treatment blood pressure, heart rate and post void residual volume to monitor for adverse effects of mirabegron therapy, and urinalysis to exclude and manage underlying urinary tract infections.

There were 26 community dwelling patients who were prescribed mirabegron with the mean age of 79 years old (ranging between 65 and 91 years old). 69% were females and 42.3% had a history of cognitive impairment. 76.9% had failed prior antimuscarinic therapy or treatment for benign prostatic hypertrophy due to ineffectiveness or adverse drug effects. Of these, 60% reported improvement of urinary symptoms with mirabegron (Figure 1). In total, 17 out of 26 patients reported improvement of OAB symptoms. All 17 patients at 3 months of follow up were on mirabegron 50 mg daily and was tolerated well. Six of the eleven patients with cognitive impairment who failed previous antimuscarinic therapy, showed improvement of OAB symptoms with mirabegron. Three patients who were on previous treatment for benign prostatic hypertrophy with combined dutasteride and tamsulosin and 1 patient on solifenacin who reported lack of efficacy, had mirabegron as an add on therapy for further management of OAB symptoms. Three of the total number of patients developed adverse effects, which included hypertension, recurrent urinary tract infections, and dry mouth respectively, and the medication was ceased as a result.

Approximately two thirds of the patients who were on previous antimuscarinic or benign prostatic hypertrophy (BPH) therapy showed improvement of OAB symptoms with mirabegron. More than 40% of our patients had a history cognitive impairment and therefore antimuscarinic was relatively contraindicated given the anticholinergic burden. Mirabegron provides a good alternative treatment choice in this particular cohort and is shown to be well tolerated. Given the provision of a hospital subsidised prescription, we better advocate for our patients to fully appreciate the effects of mirabegron for management of OAB in the lower socioeconomic. Mirabegron was well tolerated at 50 mg daily dosing in our cohort without significant adverse effects. Mirabegron improved storage symptoms in 3 patients with lower urinary tract symptoms (LUTS) secondary to prostatomegaly with the addition to combined dutasteride and tamsulosin. The addition of mirabegron to solifenacin in another patient also showed improvement in management of OAB symptoms with no reported adverse effects.

Mirabegron is effective in older patients with OAB symptoms and in those who have failed previous therapy. Mirabegron can also be considered as an add on therapy for optimisation of storage symptom in patients with LUTS and patients with OAB symptoms who are already on an antimuscarinic agent. There is low incidence of adverse effects experienced.  Mirabegron is preferred in the management of OAB symptoms for older population with multiple co-morbidities and cognitive impairment given its tolerability profile.

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