A Study to Evaluate the Efficacy, Safety and Tolerability of Mirabegron and Solifenacin Succinate Alone and in Combination for the Treatment of Overactive Bladder

Inclusion Criteria: * Inclusion Criteria at Visit 1/Screening: * Subject has a Body Mass Index (BMI) of between 18 and 35 kg/m\^2 and a total body weight between 50 and 95 kg; * Subject is willing and able to complete the micturition diary and questionnaires correctly and is willing and able to measure his/her vital signs at home at stipulated time points, using the device provided by the study personnel, and to adequately record the readings; * Subject has symptoms of overactive bladder (OAB; urinary frequency, urgency and/or urgency incontinence) for at least 3 months. * Inclusion Criteria at Visit 3/Baseline: * Subject has experienced frequency of micturition on average ≥ 8 times per 24-hour period during the 3-day micturition diary period (incontinence episode should not be counted as a micturition); * Subject must experience at least 1 episode of urgency (grade 3 or 4) per 24-hour period (with or without urgency incontinence) during the 3 day micturition diary period. Exclusion Criteria: * Exclusion Criteria at Visit 1/Screening: * Subject is breastfeeding, pregnant or intends to become pregnant during the study. The pregnancy test (Beta Human Chorionic Gonadotropin in serum) at Screening must be negative in women of childbearing potential; * Female subjects of childbearing potential and not using a highly effective method of birth control during the study and for 30 days after final study drug administration. * Male subjects (unless surgically ster…