**7. Adverse Events of BoNT-A on CPPS**

The common adverse events of BoNT-A injection into the bladder for IC/BPS are slow urinary flow rate, decreased detrusor pressure, and dysuria [39,62,63].

The most common adverse event of BoNT-A injection into PFMs for CPPS is dysuria. Increasing flatus has also been reported after BoNT-A injection into bilateral puborectalis and pubococcygeus muscles in women with chronic pelvic floor muscle spasms [14].

Adelowo et al. reported several adverse events, including retention of urine, fecal incontinence, constipation, and rectal pain after BoNT-A injection into PFMs (including coccygeus, iliococcygeus, pubococcygeus, puborectalis, obturator, and pyriformis muscles), which would be resolved spontaneously [36]. This might be because the injection sites were close to the sphincters of the urethra and anus.

Since the urethral sphincter and anal sphincter are adjacent to PFMs, BoNT-A injected into PFMs may result in disruption of urethral and/or anal sphincter mechanisms [30]. The adverse effects after BoNT-A injections reported progression of the following preexisting conditions: constipation (28.6%), stress urinary incontinence (4.8%), fecal incontinence (4.8%), and new-onset stress urinary incontinence (4.8%) [30]. Under electromyography (EMG) guidance, a needle provides more precise delivery of BoNT-A to highly spastic trigger points of the PFMs and helps with the avoidance of neighboring sphincter muscles [30].

Dressler et al. reported atrophy of target muscles after repeated injections of BoNT-A into a hyperactive muscle [64]. However, more serious side effects on systemic organs, such as respiratory failure, heart failure, weakness of muscles, or fatigue have not been reported [17].

Although most of the adverse events resulting from BoNT-A treatment are usually self-repairing, it should be clearly explained to the patient before BoNT-A injection. It is important to discuss with the patient the possibility of mild, transient, and reversible adverse effects on musculatures before BoNT-A injection.

There is still no guidelines about single injections or repeat injections, frequencies of repeat injections, an acceptable interval during repeat injections, injected sites and numbers, and maximum dosage of BoNT-A.
