Optimal Injection Interval for Intra-Detrusor Botulinum Toxin

Overactive bladder (OAB) is defined by symptoms of urinary urgency, frequency, or nocturia with or without incontinence in the absence of urinary tract infection or other attributable pathology. This disease affects up to 40% of women in the United States and can have a significant impact on quality of life. It is expected to increase in prevalence with the aging US population. There are a wide variety of treatment options for OAB which range from fluid management and lifestyle modifications (first line therapy), pelvic floor physical therapy and oral medications (second line therapy), and procedural interventions such as neuromodulation or intravesical botulinum toxin (BTX-A) injections (third line therapy).

BTX-A is a potent neurotoxin derived from the anaerobic bacterium Clostridium botulinum that inhibits presynaptic release of acetylcholine from motor neurons at the neuromuscular junction to induce flaccid paralysis of musculature. It has also been found to affect sensory responses of nerve afferent nerve fibers and likely has a complex multifactorial effect on the release of excitatory neurotransmitters. Because of this, injection of BTX-A into the detrusor muscle of the bladder has become a highly effective treatment option for OAB, first approved by the FDA in January 2013. Prior studies have demonstrated superior efficacy of intravesical BTX-A injections compared to anticholinergic medication and a greater reduction in urge urinary incontinence episodes than sacral neuromodulation.

The effect of intravesical BTX-A is temporary due to turnover of presynaptic molecules. Typical chemodenervation of muscular tissue lasts 3 to 6 months based on histologic evidence, however this does not translate directly to duration of OAB symptom control given the gradual nature of neurotransmitter repletion. The largest prior trial of intravesical BTX-A demonstrated a median interval of 350 days between first and second injection, but other studies have shown a wide range of duration from 5 to 15 months. The current FDA recommendation for repeat injection is to be "considered when the clinical effect from the previous injection has diminished" with a median interval in their double-blinded placebo-controlled studies of 169 days.

Despite this recommendation, there is a wide variety in practice patterns for repeat injections, including the use of a "one size fits all" approach with standardized repeat injections at 6-month intervals. Combined with varying rates of tolerability and treatment failure, this has resulted in inconsistent data on continuation and dropout rates for repeat injections, with reported continuation rates of 20-60% in different studies. Additionally, no prior studies have reported whether repeat injection intervals have been provider- or patient-determined, nor with data on patient satisfaction ratings. Further studies are needed to better delineate optimal injection interval as well as incorporate data on what methods lead to the highest patient satisfaction and symptom control.

The purpose of this study is to ascertain the optimal time interval to repeat injection will be when it is purely patient directed based on symptomatology. Investigators will also evaluate patient satisfaction with this approach compared to standardized repeat injection interval of six months. This has the potential to change the way OAB is managed by allowing patients to control the interval to repeat injection in a safe and controlled manner. Investigators hypothesize that a patient-centered approach to repeating BTX-A injections will be similar to the standard FDA 6-month interval while leading to higher patient satisfaction and continuation rates without compromising safety or efficacy.

Inclusion criteria

• diagnosis of overactive bladder, detrusor overactivity, urinary urgency, urinary frequency, nocturnal polyuria, or urge urinary incontinence
• pursuing treatment with intravesical botulinum toxin injections

Exclusion criteria

• non-OAB diagnosis such as pelvic pain or interstitial cystitis