Oxybutynin for Post-surgical Bladder Pain and Urgency

Pain after bladder surgery is typically controlled with narcotics, non-steroidal anti-inflammatory medications, acetaminophen, regional anesthesia (caudal or epidural) and/or bladder muscle (detrusor) antispasmodic medication. It is often difficult to distinguish bladder pain from a sensation of urinary urgency and most likely patients are experiencing both sensations despite the bladder being empty from the indwelling catheter.

Prior studies on adults have demonstrated the efficacy of preoperative oxybutynin and other antimuscarinics on decreasing catheter-related bladder discomfort in the postoperative period. For pediatric bladder surgery very few studies have been published. Intravenous ketorolac, epidural and caudal analgesia and intravesical ropivacaine have been shown to decrease postoperative bladder spasms. Intravesical oxybutynin has been used in the operating room in adults to decrease post-operative ureteral stent pain.

For open bladder surgery the current pain management standard is intra- and postoperative ketorolac (Q6hrs) and acetaminophen and narcotic as needed. Oral oxybutynin is started pre-operatively and then continued post-operatively every 8 hours. Unfortunately, the bioavailability of oral oxybutynin is poor due to first pass (liver) metabolism of the absorbed medication and a subsequent high level of desethyloxybutynin (DEO) produced by the liver. DEO, responsible for most of the side effects such as dry mouth, dizziness, over-heating, drowsiness and constipation. This metabolite and side effects are less with the transdermal route.

A prior retrospective analysis of children by the investigators did not show a difference in pain between starting oral oxybutynin pre-operatively or initiating medication post-operatively. Whether this was due to no difference, insufficient patient numbers or inability to distinguish bladder spasms from pain is unknown. That study employed the Wong-Baker-Facies scale for pain measurement in children. At the time of that study there was no valid scale for objective measurement of bladder urgency in adults or children. Over the last five years the investigators have developed a validated scale (IRB 647657, 638967) that will allow for a better measure and distinguish bladder and incisional pain from bladder spasms/urgency.

The objective is to determine if transdermal administration is superior to oral administration in alleviating pain and urgency after bladder surgery in children. Oral oxybutynin is a commonly used treatment in children with neuropathic bladder dysfunction and for adults with overactive bladder (OAB) and incontinence. As mentioned, transdermal administration has higher bioavailability and a lower adverse event profile. Transdermal administration has been shown to be safe and efficacious in children with neuropathic bladder disease. The hypothesis is that the transdermal route will decrease bladder pain and urgency if applied prior to surgery with a lower side effect profile.

Based upon the power analysis by Blythe Durbin-Johnson, Ph. D. The investigators plan to evaluate up to 100 patients with early termination if endpoints are reached before 100 subjects.

Outcomes will be compared between groups using two-sample t-tests if the outcome is sufficiently normally distributed, and Wilcoxon-rank sum tests otherwise. With 60 subjects divided among two groups, the two-sample t-test will have 80% power to detect a 0.74 standard deviation difference in outcomes.