Describe botulinum toxin A therapy for detrusor overactivity and a common adverse effect.

• A. Oral botulinum toxin A to reduce detrusor contractions; common side effect is dizziness.
• B. Intravesical botulinum toxin A injections into the detrusor; commonly 100 U; can cause urinary retention requiring intermittent catheterization.
• C. Topical botulinum toxin A applied to the urethra; common side effect is urethral bleeding.
• D. Intravenous botulinum toxin A to paralyze the detrusor; common side effect is hypertension.

Answer: (B)

Botulinum toxin A helps detrusor overactivity by blocking acetylcholine release from the parasympathetic nerves controlling the bladder. This reduces involuntary detrusor contractions and increases bladder capacity, improving storage symptoms.

Delivery is intravesical: the toxin is injected directly into the detrusor muscle via cystoscopy, usually about 100 units total divided among multiple injection sites. This targeted delivery is essential because systemic or non-bladder routes won’t reliably treat the overactivity.

A key adverse effect is urinary retention requiring intermittent catheterization. By dampening detrusor activity, the bladder may not empty efficiently, leading to increased postvoid residuals in some patients. Other possible side effects include urinary tract infections and dysuria, but urinary retention is the most characteristic and clinically important risk.

Oral, topical, or intravenous approaches are not appropriate for this purpose because they don’t deliver the toxin to the detrusor in a way that reliably reduces overactivity, and they carry different or increased risks.