Mixed evidence exists regarding the influence of age on the efficacy of intravesical OnabotulinumtoxinA (BTX). This study aims to determine whether age independently predicts therapeutic success, durability, retention, adverse events, discontinuation, and correlates of with response to BOTOX.

Retrospective cohort study of patients receiving first BTX injection (2018 to 2025). Patients were stratified by WHO age groups: Adolescent (15‑24), Young Adult (25‑44), Middle Age (45‑59), Elderly (60‑74), Senior (75+). The primary outcome was therapeutic efficacy, analyzed both as binary (improvement in ≥1 of symptoms, incontinence, or CIC reduction) and as ordinal. Secondary outcomes included durability (time to symptom recurrence, Kaplan‑Meier), impact of detrusor overactivity (DO), predictors of improvement (pre‑BTX creatinine, GFR, hydronephrosis, bladder capacity, impaired compliance, DLPP>40, pharmacotherapy), de novo retention rate, UTI rate, discontinuation rate, relationship with subsequent injections and dose increase, and correlation of improvement with age, gender, neurogenic etiology, comorbidities, pharmacotherapy, urodynamic parameters, and total number of  injections. Multivariable logistic regression and Kruskal‑Wallis were used, adjusting for gender, neurogenic etiology, DO, impaired compliance, and bladder capacity.

We found 111 patients, 73.0% achieved improvement. Improvement decreased with age (p = 0.036). On multivariable analysis, the Elderly group (60‑74) was significantly less likely to improve thanAdolescent (OR 0.29; 95% CI 0.08 0.99; p = 0.048). The degree of improvement declined with age (p = 0.021). Kaplan‑Meier analysis showed shorter median time to recurrence in the Elderly group (4 months) versus Adolescent (10 months;  p = 0.028). The effect of age on improvement did not differ by DO status (interaction p = 0.62). Pre‑BTX hydronephrosis was an independent negative predictor of improvement (OR 0.20; 95% CI 0.05 0.85; p = 0.028). De novo retention occurred in 31% of patients not already on CIC, with a non‑significant trend toward higher rates in older groups (Elderly 42.9% vs. Young Adult 24.6%, p = 0.21). UTI rates were highest in the Elderly (50.0% vs. 26.3% in Adolescent, p = 0.12). Discontinuation rates increased with age (Elderly 28.6% vs. Adolescent 10.5%, p = 0.10), reaching 50% in Seniors (n=2). In patients with 1 subsequent injection or more, dose increase was associated with worse improvement (OR 3.6; 95% CI 1.1 11.8; p = 0.03). Total injections showed a weak negative correlation with improvement ( p = 0.07). Univariate correlations identified significant associations between improvement and age (p = 0.035), neurogenic etiology (p = 0.041), pre‑BTX hydronephrosis (p = 0.020), dose increase (p = 0.006), and discontinuation ( p < 0.001). Gender, comorbidities, pharmacotherapy, DO, impaired compliance, DLPP>40, bladder capacity, creatinine, and GFR did not show significant associations.

These findings suggest that older age (≥60 years) can independently predict lower efficacy, shorter duration of efficacy (4 vs. 10 months), and higher discontinuation rate after injection. Pre‑BTX hydronephrosis signals poor response. These findings the importance of shared decision‑making in older patients.

Advanced age (≥60 years) independently predicts lower likelihood and lesser degree of symptom improvement, shorter durability, and higher discontinuation after intravesical BTX. Pre‑BTX hydronephrosis is a negative predictor and dose escalation may signal failure. These findings should emphasize shared decision‑making when offering BTX to older patients.