Intravesical OnabotulinumtoxinA is becoming a well-used tool for management of overactive detrusor refractory to medical management, with efficacy well documented (1, 2). Allergan® report a rate of urinary retention requiring intermittent catheterization (IC) at approximately 6% for patients post treatment of idiopathic detrusor overactivity (1). Despite this classically reported risk, other randomized controlled trials report rates of IC between 4.3% - 43% (2). This study aims to review the experience of a specialist urological surgeon to assess if current quoted rates of urinary retention are in line with prior experiences; as well as to identify preoperative predictors for retention to help guide future consent and patient management.

A retrospective review of a single Australian urologist was completed. All female patients who underwent intravesical OnabotulinumtoxinA for management of idiopathic detrusor overactivity were included. Patient data was collected from February 2016 to March 2021. Patients were not included if they did not have a complete preoperative urodynamic assessment available for analysis, or if a patient was lost to follow up.  

Patient demographics, significant past medical history, urodynamic assessment and post-operative post-void residual (PVR) was recorded. 

The two primary outcomes were PVR post 100units of intravesical OnabotulinumtoxinA and the other was identifying rate of intermittent catheterisation within this cohort. Post void residual was measured between 2-4 weeks post operatively. Initiation of intermittent catheterization was dependent upon PVR and clinical concern for poor effective bladder emptying, i.e if the surgeon was convinced void volume was significant in relation to PVR intermittent catheterization was withheld, conversely a relatively “low” PVR with small volume voids could have intermittent catherization commenced. This is in direct contrast to prior Allergan® data which determined need of IC on PVR, where depending on the patient symptoms, the investigator could initiate IC at a PVR volume between ≥200 and <350mL with patients PVR above 350mL IC was to have been initiated regardless of patient symptoms. 

Secondary outcomes looked at predictive factors for elevated post voids postoperatively.

Data collection is ongoing and we publish interim results.

From our study we found 77 female patients who qualified for inclusion, with a mean age of 70 years (18-95 years). In total 126 procedures were performed in this cohort with intravesical injection of 100 units of OnabotulinumtoxinA. The average first post-operative PVR was 157.7ml (range 0 – 1139ml). 

Postoperatively, 23 (30%) patients experienced urinary retention with clinical concern for incomplete bladder emptying resulting in initiation of intermittent catheterization. The mean PVR for these patients was 443ml (range 150-1139ml). Mean duration of intermittent catherization was 11 weeks (1-36 weeks), with four patients preferring indwelling catheterisation. Patients who had a preoperative PVR of <100ml demonstrated a similar rate of retention (29%). 

In total 54 (70%) patients were deemed clinically safe to avoid intermittent catheterization with an average PVR 105ml (range 0-478ml) within this cohort.

Predictive factors from preoperative urodynamics are shown in Table 1 with preoperative demographic and comorbity predictors shown in Table 2.

We have identified a higher than expected rate of requirement of intermittent catheterization with 30% within our cohort compared to quoted 6% in Allergan® material, this is despite our surgical experience having more tolerance for comparatively elevated post void residuals. 

Within our cohort age and preoperative PVR did not appear to be a predictive factor, where as patients requiring intermittent catheterization had an increased rate (25% compared to 9%) of preoperative urinary tract infection, despite adequate antimicrobial treatment.

We acknowledge limitations of this study include single surgeon cohort but believe it is one of the largest comparative datasets looking at rates of intermittent catheterization for females with idiopathic detrusor overactivity. Simple statistics were used for comparative analysis but we hope to use multivariate logistic regression to assess statistical significance of predictive factors.

These results are in line with other internationally recognised studies with similar rates of intermittent catheterization post 100units OnabotulinumtoxinA (3), which are up to six times those reported from Allergan®. Further studies should look to larger cohorts, preferably multisite analysis to see if this trend is more prevalent within urological practice. We suggest further investigation into preoperative assessment, such a max flow and absence of obstruction on urodynamics may be protective factors for patients wishing to have an accurate risk profile preoperatively.

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