Mirabegron, the first selective beta(3)-adrenoceptor agonist for the treatment of overactive bladder (OAB), inhibits cytochrome P450 isozyme CYP2D6. This study was performed in Japanese healthy postmenopausal female volunteers to assess any pharmacokinetic drug interaction between mirabegron and tolterodine, another OAB drug and a sensitive substrate of CYP2D6. Tolterodine 4 mg was orally administered from Days 1-7 and co-administered with mirabegron 50 mg from Days 8-14. Mirabegron 50 mg increased maximum concentration (C-max) and area under the concentration-time curve from zero to 24 h after dosing (AUC(24h)) of tolterodine by 2.06-fold (90% confidence interval [CI] 1.81, 2.34) and 1.86-fold (90% CI 1.60, 2.16), respectively, and increased Cmax and AUC24h of the metabolite 5-hydroxymethyl tolterodine by 1.36-fold (90% CI 1.26, 1.47) and 1.25-fold (90% CI 1.15, 1.37), respectively. This suggested a weak pharmacokinetic drug interaction between mirabegron and tolterodine. Mean change from baseline of Fridericia's QT correction formula (Delta QTcF) was slightly higher on Day 14 than on Day 7. No subject had QTcF >480 msec or Delta QTcF >60 msec. All the treatment-emergent adverse events were mild. Mirabegron 50 mg was considered to be safe and well tolerated when coadministered with tolterodine 4 mg in healthy postmenopausal female volunteers. (C) 2016 The Japanese Society for the Study of Xenobiotics. Published by Elsevier Ltd. All rights reserved.