Severe urinary incontinence is a significant problem that increases with age. Around 5% of Australians aged 65 to 84 years are thought to be affected, with incidence increasing to 28% for those aged over 85 years. Appropriate management is important as incontinence can have a significant impact on quality of life. Potential complications of urinary incontinence include skin infections, decubitus ulcers, falls, depression, poor self-confidence, and a loss of independence.

Urinary urge incontinence occurs due to overactivity of the detrusor muscle which causes the bladder to contract before it is full. Pharmacotherapy for this condition often relies on anticholinergic agents such as oxybutynin and solifenacin. However, these agents have significant side effects, to which the elderly are particularly susceptible.

Mirabegron may be considered for patients who cannot take anticholinergics due to contraindications, poor tolerance, or a lack of efficacy. Mirabegron is a β3-adrenoceptor agonist that relaxes the detrusor muscle to increase bladder storage capacity and reduce voiding frequency. Clinical trials demonstrate modest efficacy with an average of 0.8 fewer incontinence episodes over 48 hours for mirabegron 50mg compared to placebo. Statistically significant improvements were also observed for the mean number of micturitions per day, and the mean volume voided per micturition.

While mirabegron is selective for β3-adrenoceptors, some stimulation of β1 and β2-adrenoceptors can occur. This may result in cardiac adverse effects including increased blood pressure and pulse rate. Caution is recommended for patients with hypertension, while mirabegron therapy is contraindicated in patients with severe uncontrolled hypertension.


  1. Australian Government. Leading causes of ill health. In: Australia’s Health 2016. Canberra: Australian Institute of Health and Welfare; 2017.
  2. Betmiga® (Mirabegron) Australian approved product information. Macquarie Park: Astellas Pharma Australia Pty Ltd. Approved January 2017.
  3. Khullar V, Amarenco G, Angulo JC, Cambronero J, Hoye K, Milsom I, et al. Efficacy and tolerability of mirabegron, a β3-adrenoceptor agonist, in patients with overactive bladder: results from a randomised European–Australian phase 3 trial. Eur Urol. 2013; 63(2): 283-95.

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