Fesobig 4 Tablet ER is an antispasmodic medicine used to treat overactive bladder in adult patients. It relaxes the bladder muscles and improves their ability to control urination. It also helps to reduce urine leakage and feelings of needing to urinate right away.Fesobig 4 Tablet ER may be taken with or without food. However, take it in the dose and duration prescribed by your doctor to get the most benefit. It is also advised to take this medicine at the same time each day to avoid missing a dose.