Overactive Bladder (OAB) is characterized by disruptive urinary symptoms, including the sudden, compelling urge to urinate (urgency), frequent urination, and involuntary leakage of urine (urge incontinence). These symptoms arise from the detrusor muscle, the main muscle in the bladder wall, contracting involuntarily and prematurely. For people whose symptoms have not improved with standard treatments, a specific formulation of botulinum toxin type A, known as onabotulinumtoxinA (Botox), has been approved as a targeted, third-line therapy. This injection is used when initial approaches like behavioral changes and oral medications have proven ineffective or caused intolerable side effects.
How the Treatment Works and Patient Eligibility
The injection of onabotulinumtoxinA targets the overactive detrusor muscle within the bladder wall. The toxin temporarily blocks the release of acetylcholine, the primary neurotransmitter responsible for signaling the muscle to contract. By inhibiting this signal at the nerve endings, the medication reduces the frequency and strength of involuntary bladder spasms that cause urgency and incontinence. This action relaxes the bladder muscle, allowing it to store urine more efficiently and increasing its functional capacity. The toxin also modulates the sensory signals that transmit the feeling of urgency from the bladder to the brain. This treatment is reserved for adults with OAB who have not responded adequately to or cannot tolerate at least two different classes of oral OAB medications, such as anticholinergics or beta-3 agonists.
What Happens During the Injection Procedure
The injection procedure is performed on an outpatient basis and does not require general anesthesia. The patient’s urethra and bladder are first numbed using a local anesthetic, such as lidocaine, which remains in the bladder for about 20 to 30 minutes. A urologist then inserts a thin, flexible instrument called a cystoscope through the urethra to visualize the bladder.
Using a fine needle passed through the cystoscope channel, the physician performs a series of injections directly into the detrusor muscle. The standard dose of 100 units is divided into approximately 20 separate injection sites across the bladder wall, carefully avoiding the trigone area. The actual injection process often takes less than five minutes.
Following the procedure, patients are monitored briefly and asked to urinate before discharge. It is common to experience temporary discomfort, a burning sensation during urination, or blood in the urine (hematuria) for a few days. Patients can return to their normal activities shortly after leaving the office.
Typical Results and Duration of Effect
The effects of the onabotulinumtoxinA injection are not immediate; most people notice initial symptom relief within one to two weeks, with maximum effectiveness peaking between two and eight weeks post-treatment. Clinical trial data show that this treatment provides significant improvements in OAB symptoms, including a substantial reduction in daily urge urinary incontinence episodes. Approximately two-thirds of patients report a positive response, leading to an improvement in their overall quality of life.
The therapeutic effect is temporary because the nerve endings eventually regenerate. On average, the benefits of a single injection last between six and nine months. Follow-up injections are necessary to maintain symptom control when benefits begin to diminish. The FDA recommends a minimum interval of 12 weeks between injections. Repeat treatments have not shown a decrease in effectiveness over time, offering a durable long-term management strategy for refractory OAB.
Understanding the Potential Side Effects
The treatment carries a risk of specific adverse events that patients must understand before proceeding. The most significant side effect is urinary retention, the inability to fully empty the bladder. This occurs because the muscle-relaxing effect of the toxin may temporarily weaken the detrusor muscle too much.
Patients who develop retention may require temporary reliance on clean intermittent catheterization (CIC). This involves the patient learning to insert a small tube to drain the bladder multiple times daily until the medication’s effect lessens. The necessity for self-catheterization is relatively low in idiopathic OAB patients, affecting about 6% of patients in clinical trials, and is usually transient, lasting a median of about 63 days.
Other common side effects include an increased risk of developing a urinary tract infection (UTI), which occurs in up to 18% of patients, and transient blood in the urine immediately following the procedure. To mitigate the risk of infection, doctors often prescribe a short course of prophylactic antibiotics around the time of the injection. Patients are thoroughly counselled on the risk of retention and the need for CIC before the procedure, as only those willing and able to perform it should receive the injection.