When given intravesically, your body absorbs little or none of the drug, making systemic reactions rare. Allergic reactions can occur in 3% to 19% of patients. Rarely, some patients will experience decreased blood cell counts. Also, some researchers have reported a decreased bladder capacity (the volume of urine a bladder can hold).
The most common side effect is discomfort during urination (dysuria) and the frequent need to urinate (frequency). This can occur in as many as 41% of patients, but it usually goes away over a few days. Occasionally, these symptoms can last several weeks. Overall, most patients tolerate it very well and have minimal problems.