Pharmacodynamics
Botulinum toxin type A blocks the peripheral release of acetylcholine at presynaptic cholinergic nerve terminals by cleaving SNAP-25, an integral component involved in the binding and release of acetylcholine from vesicles located at nerve endings.
After injection, the toxin rapidly binds to surface receptors of specific cells. This is followed by internalization of the toxin via receptor-mediated endocytosis through the plasma membrane. The toxin is then released into the cytosol. This final process is associated with a gradual decrease in acetylcholine release. Clinical signs typically appear within 2–3 days, and the maximum effect is observed approximately 5–6 weeks after injection.
Recovery after intramuscular injection occurs over approximately 12 weeks, as nerve endings regenerate and re-establish connections with the motor endplate. After subcutaneous injection, when the target is the axillary sweat glands, patients who received 50 Units of Allergan’s Botox in each axilla experienced effects lasting from 7.5 months up to 1 year or more. However, in 27.5% of patients, the effect lasted 1 year or longer.
The regeneration of sympathetic nerve terminals innervating sweat glands after subcutaneous injection has not been studied. When injected into the detrusor muscle, Botox acts on efferent pathways of detrusor activity by inhibiting the release of acetylcholine. Botox may also inhibit afferent neurotransmitters and sensory pathways.
 
Clinical Study Data
Idiopathic Overactive Bladder
Two randomized, double-blind, placebo-controlled, parallel-group, multicenter phase III clinical trials were conducted in patients with overactive bladder (OAB) symptoms, including urinary incontinence, urgency, and frequency, over a study duration of 24 weeks.
A total of 1,105 patients were enrolled who had not achieved adequate relief from at least one anticholinergic medication due to either insufficient efficacy or unacceptable side effects. These patients were randomized to receive either Botox 100 Units (Allergan) (557 patients) or placebo (548 patients).
In both studies, significant improvements (versus placebo) from baseline in the primary efficacy endpoint—measured by the frequency of urinary incontinence episodes per week—were observed in favor of Botox 100 Units (Allergan) during the primary efficacy interval at week 12 (5.49 episodes in the Botox group vs. 5.39 in the placebo group), including the percentage of “dry” patients.
Using the Treatment Benefit Scale, a significantly greater number of patients in the Botox group reported positive treatment outcomes ("greatly improved" or "improved") compared to the placebo group.
Botox treatment was also associated with significantly greater reductions in symptoms such as urinary frequency, urgency, and nocturia compared to placebo. The average volume of urine per void was also significantly increased. Notably, significant improvement in symptoms of overactive bladder was observed from week 2 onwards.
Botox treatment led to significantly greater improvements compared to placebo in health-related quality of life, as measured by the Incontinence Quality of Life (I-QOL) questionnaire—including behavioral avoidance, psychological impact, and social embarrassment—and by the King's Health Questionnaire (KHQ), which covers domains such as incontinence impact, role limitations, social limitations, physical limitations, personal relationships, emotions, sleep/energy, and severity measures of psychological adaptation.
No significant differences in efficacy were observed between patients aged ≥65 years and those <65 years.