Adverse Events of Intravesical OnabotulinumtoxinA Injection between Patients with Overactive Bladder and Interstitial Cystitis—Different Mechanisms of Action of Botox on Bladder Dysfunction?

Intravesical onabotulinumtoxinA (BoNT-A) injections have been proposed to treat both overactive bladder (OAB) and interstitial cystitis/bladder pain syndrome (IC/BPS) in patients with refractory conditions. We compared adverse events (AEs) after BoNT-A treatment between IC/BPS and OAB in women. IC/BPS patients who failed conventional treatments were enrolled to receive suburothelial injections of BoNT-A (100 U) followed by hydrodistention. Age matched OAB female patients refractory to antimuscarinic agents underwent BoNT-A (100 U) injections. The bladder capacity, maximum flow rate (Qmax), post-void residual (PVR), and voiding efficiency (VE) at baseline, 3 and 6 months, and the post-treatment AEs were analyzed between groups. Finally, 89 IC/BPS and 72 OAB women were included. In the OAB group, the bladder capacity and PVR increased, and VE decreased significantly at three and six months after BoNT-A treatment. In the IC/BPS group, the Qmax increased significantly at six months. There were significant differences in changes of capacity, Qmax, PVR and VE between the two groups. Moreover, OAB patients suffered more frequently from events of hematuria, UTI, and large PVR (>200 mL), but less frequently from events of straining to void. In conclusion, OAB women had higher PVR volume and lower VE than those in IC/BPS after BoNT-A injections. These results imply that the bladder contractility of OAB patients are more susceptible to BoNT-A, which might reflect the different mechanisms of action of Botox on bladder dysfunction. Further investigations to confirm this hypothesis are warranted.