*5.2. Intervention*

#### 5.2.1. Submucosal Injection of BoNT/A

All the patients received a submucosal injection of BoNT/A (Lanzhou Biotechnology Development Co., Ltd., Lanzhou, China) under continuous epidural anesthesia. An amount of 200 U of BoNT/A was diluted in 20 mL of sterile saline in advance, resulting in 10 U of BoNT/A per 1.0 mL. The submucosal injection areas included the left, right, anterior and posterior bladder walls, sparing the trigone. Each of these four bladder walls was injected six times with 8 U of BoNT/A per injection. As dysuria was a common complication and urinary retention was a severe complication, catheterization was routinely applied and removed about 5 days after the operation. An oral antibiotic agen<sup>t</sup> was prescribed for 7 days. Afterwards, the patients in the Mix group accepted intravesical instillation of Sapylin.

#### 5.2.2. Intravesical Instillation of Sapylin

One week after the operation, all patients in the Mix group began to receive intravesical instillation of Sapylin (Sinopharm Group Luya (Shandong) Pharmaceutical Co., Ltd., Jining, China). Sapylin 5 KE (a unit of measure) was evenly dissolved in 40 mL of sterile saline. Mixed Sapylin was instilled into the bladder through a urinary catheter, which was removed after injection, and the Sapylin remained in the bladder until the occurrence of pelvic pain or discomfort but for no more than 2 h. It was instilled once a week within 6 weeks post-injection, then, once every 4 weeks for 2 years, totaling 29 intravesical doses.

## *5.3. Statistical Methods*

The continuous variables are expressed as the mean value (standard deviation) and median [Min, Max] and the differences among groups were compared by Student's t-tests (normal distribution) or Mann–Whitney U test (non-normal distribution). In addition, categorical variables are represented as counts or percentages and the inter-block comparison was analyzed with a chi-squared test. A *p* value of <0.05 was considered statistically significant. SPSS version 26.0 (IBM, Armonk, NY) and MedCalc (MedCalc Software bvba) were used for the statistical analysis.

**Author Contributions:** Conceptualization, Y.Y.; Data curation, C.Z. and K.L.; Formal analysis, W.L., Z.Z. and K.M.; Funding acquisition, Y.Y.; Investigation, W.L., Z.Z. and K.M.; Methodology, Y.Y.; Resources, W.L., Z.Z., K.M. and P.T.; Software, C.Z. and K.L.; Supervision, Y.Y.; Validation, C.Z. and K.L.; Visualization, C.Z. and K.L.; Writing—original draft, W.L., Z.Z. and K.M.; Writing—review and editing, P.T. and Y.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by the Natural Science Foundation of Guangdong Province (2016A030313300) and Guangdong Provincial Clinical Research Center for Urological Diseases (2020B1111170006).

**Institutional Review Board Statement:** This retrospective study was approved by the Ethics Committee of the Sun Yat-sen Memorial Hospital of Sun Yat-sen University (Approval number: SYSEC-KY-KS-2022-156, Date: 11 May 2022) and performed following the 1975 Declaration of Helsinki, revised in 2013.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available.

**Acknowledgments:** We are grateful to the nurses and staff of Sun Yat-sen Memorial Hospital, as well as the patients involved in this study. Additionally, we are very grateful to the reviewers of our manuscript. We appreciate the providers of the grants; they were not involved in the writing of this manuscript.

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