This was a prospective, randomized, single-blinded clinical study conducted at University Medical Centre Maribor between August 2018 and November 2022. National Medical Ethics Committee approval was obtained (approval number 0120-44/2018/5; date of approval 22 February2018). The study was retrospectively registered at ClinicalTrials.gov (ClinicalTrials.gov Identifier: NCT06250543, date of approval: 8.2.2024).

The primary aim of the study was to compare the efficacy of abobotulinumtoxinA and incobotulinumtoxinA treatment in women with OAB by evaluating the UDI‑6, IIQ‑7, and I‑QOL pretreatment and posttreatment scores.

The secondary aim of the study was to evaluate the effect of lidocaine instillation on the pain level during the procedure by evaluating the VAS score for patient satisfaction with the treatment, and to compare the occurrence of side effects between groups (urinary retention, urinary tract infections, UTI).

We included female patients with refractory OAB in whom previous treatment was unsuccessful and were planned for therapy with BoNT injection. The inclusion criteria were the following: female, age between 18 and 90 years, presence of urinary urgency with urgency urinary incontinence, residual urine below 150 ml, previous nonpharmacological conservative treatment inefficiency, anticholinergic or beta‑3 agonist treatment inefficiency.

The exclusion criteria were previous treatment with BoNT, pregnancy or breastfeeding, stress urinary incontinence (SUI), and any diseases or functional abnormalities that might affect bladder function (bladder stones, bladder tumors, bladder diverticula, demyelinating disease, Parkinson’s disease, spinal lesion, cerebral infarction, etc.). All patients signed the informed consent form prior to inclusion in the study.

Before treatment, each patient underwent a medical history and physical examination. Before BoNT injection, each patient completed three standardized questionnaires: Urogenital Distress Inventory (IU-6), Incontinence Impact Questionnaire (IIQ-7), and Incontinence Quality of Life (I-QOL). Each patient reported urinary incontinence episodes, frequency and nocturia before and 4 months after treatment. To extensively quantify the influence of UI, it is necessary to measure the level of symptoms of an individual and the magnitude to which they compromise their life. In urogynecology the utilization of questionnaires to measure outcomes has been increasing. The UDI‑6 and IIQ‑7 are well-known broadly used condition-specific questionnaires [17]. Urine dipstick test was routinely performed to exclude urinary tract infection (UTI). For all of the patients with UTI, treatment was rescheduled, the UTI was treated and another urine dipstick test was carried out. Patients were randomly assigned to one of two study arms by computer using an allocation ratio of 1:1. After BoNT treatment, the patients were invited to a follow-up visit after 1–2 weeks for systemic side effects evaluation, physical examination, measurement of residual urine, and urine dipstick test to diagnose and treat UTI. After 4 months, patients were seen to evaluate the treatment result and complete the IIQ‑7, UDI‑6, patient satisfaction, and I‑QOL questionnaires. Side effects were monitored for 5 months after the procedure.

The UDI‑6 is a questionnaire that comprises 6 items: “1—Frequent urination, 2—Leakage related to feeling of urgency, 3—Leakage related to activity, 4—Coughing or sneezing small amounts of leakage (drops), 5—Difficulty emptying the bladder, and 6—Pain or discomfort in the lower abdominal or genital area.” The scores range from 0 to 100. The higher the scores, the higher the disability of the patient [18]. Scores higher than 33.33 indicate higher distress caused by UI symptoms [17].

The IIQ‑7 is a questionnaire that comprises 7 items: “1—Household chores, 2—Physical recreation, 3—Entertainment activities, 4—Travel > 30 min away from home, 5—Social activities, 6—Emotional health (nervousness, depression, etc.), 7—Feeling frustrated.” The higher the scores, the higher the disability of the patient. The total score ranges from 0 to 100 [19]. Women who scored 9 or more on the IIQ‑7 questionnaire felt an impaired quality of life [17].

The I‑QOL is a questionnaire that evaluates the influence of urinary incontinence on health-related QOL. It comprises 22 items divided into 3 domains: an 8‑item domain evaluating the physical impact, a 9-item domain evaluating the psychological impact, and a 5-item domain evaluating the social impact. For all 22 items a total score is calculated, also for each domain scores are calculated. The scores range from 0 to 100. The higher the scores, the better the health status of the patient [5, 20].

Patient satisfaction was assessed using a 5-point scale: 1—very dissatisfied, 2—partially satisfied, 3—moderately satisfied, 4—very satisfied, and 5—exceptionally satisfied.

The procedure was performed in an outpatient clinic. For antibiotic prophylaxis nitrofurantoin 100 mg twice daily per os was given on the day of the procedure. Patients were randomized to receive either 300 units of abobotulinumtoxinA (Dysport®) or 100 units of incobotulinumtoxinA (Xeomin®). They were further randomized to receive instillation anesthesia or placebo. The bladder was instilled with either 40 ml 1% lidocaine solution using a 16 Fr urethral Foley catheter or 40 ml 0.9% NaCl solution 30 min before the procedure. All patients received urethral lubrication gel containing lidocaine. Using rigid cystoscopy, 20 ml of normal saline was used to dilute each vial. A total of 20 evenly distributed intradetrusor injections were administered. Each site was injected with 1 ml and 2 injections included the trigone area. During the procedure, the patients scored the pain intensity of every injection on a visual analog scale (VAS). All procedures were performed by one experienced surgeon.

For this non-inferiority trial, a group sample size of 64 subjects was required to reach 80% power of the test with a significance level (alpha) of 0.05. The clinically important non-inferiority limit for the UDI‑6 questionnaire was set at 18. The expected difference between the means of both treatments was assumed to be 0 [17, 21]. The sample size was calculated by using Sealed Envelope Ltd. 2012. Power calculator for continuous outcome non-inferiority trial.

Statistical analysis was performed using SPSS (Version 29.0, IBM, Armonk, New York, United States). Basic patient characteristics were calculated using elemental descriptive statistics. Non-parametric statistical tests were used to compare data between groups. Continuous data from independent samples were analyzed using the Mann-Whitney U test, whereas comparisons of continuous data within matched samples employed the Wilcoxon signed-rank test. In all analyses, a two-sided p-value < 0.05 was considered significant. Considering the multiple hypotheses being tested in the study (a total of 10), the Bonferroni correction was applied to adjust for multiple comparisons.