Mirabegron is a potent and selective agonist for beta-3 adrenergic receptors. Once beta-3 receptors are activated, the detrusor smooth muscle relaxes to allow for a larger bladder capacity. At higher doses (200 mg), there is a potential for mirabegron to activate beta-1 and beta-2 adrenergic receptors.
Mirabegron has little effect on the mean maximum flow rate or mean detrusor pressure at maximum flow rate in patients with lower urinary tract symptoms and bladder outlet obstruction. Furthermore, mirabegron increases blood pressure in a dose dependent manner. However, this effect is reversible when mirabegron is discontinued. Mirabegron also increases heart rate in a dose dependent manner. The dose in which half-maximal efficacy is demonstrated is 25 mg. Comparatively, the dose in which maximal efficacy is demonstrated is 100 mg.
Mirabegron is metabolized via multiple pathways involving dealkylation, oxidation, (direct) glucuronidation, and amide hydrolysis. The major circulating entity is mirabegron. Two major and inactive metabolites (phase 2 glucuronides) are produced. Although mirabegron is a substrate for CYP2D6 and CYP3A4, its role in the elimination of the drug is limited. Studies also suggest that CYP3A4 is the main enzyme that facilitates the oxidative metabolism of the drug. Furthermore, butylcholinesterase, uridine diphospho-glucuronosyltransferases (UGT), and possibly alcohol dehydrogenase may be involved with the metabolism of mirabegron.
Most commonly reported adverse reactions (> 2% and > placebo) were hypertension, nasopharyngitis, urinary tract infection and headache