How are b3 agonists in UUI?

They achieve inhibition of spontaneous contractile activity in the bladder and reduction in bladder afferent activity.  Mirabegron is the first of its class and the only beta-3 adrenoceptor agonist that is used as a second-line treatment for those who either poorly tolerate antimuscarinic agents or cannot tolerate them at all. Daily doses of mirabegron 25, 50, and 100 mg demonstrated significant efficacy in treating symptoms of urge incontinence in phase three clinical trials. In some cases, combining an anticholinergic medication with mirabegron may result in increased efficacy and minimized side effect load. This medication can theoretically lead to an increase in cardiovascular events, particularly hypertension and headache.