**4. Conclusions**

Intravesical BoNT-A injection provides a promising option in treating IC/BPS. Randomized placebo-controlled trials have revealed that intravesical BoNT-A injection is effective for relief of pain and urinary symptoms. The mechanisms by which BoNT-A is effective for treatment of IC/BPS include inhibition of detrusor muscle activity, as well as directly sensory modulation and inflammation control in the urothelium. Although current guidelines consider BoNT-A injection to be the standard treatment, some practical issues remain. Most clinical evidence comes from retrospective uncontrolled studies, and there are only two randomized, placebo-controlled studies with limited patients numbers to support BoNT-A efficacy in IC/BPS. Most patients with IC/BPS experience symptom relapse at six to nine months after BoNT-A injection, although repeated BoNT-A injections have persistent therapeutic

effects. The optimal BoNT-A injection dose and site have not been well-investigated in comparison studies. For the IC/BPS patients with Hunner's lesion, clinical efficacy is still unclear. Further high-level evidence studies with greater numbers of patients are necessary to support using BoNT-A injection as a standard treatment for patients with IC/BPS.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflicts of interest.
