Purpose: To examine the factors of intravesical oxybutynin influencing the cystometrogram in normal conscious rats at various pH levels and concentrations of oxybutynin.
Materials and methods: A cystostomy catheter was implanted into the bladders of male Sprague-Dawley rats. We compared the urodynamic effects of intravesical oxybutynin dissolved in pH 4.44, 6.44 and 8.44 buffer. Two concentrations of oxybutynin solution were adopted, 0.06 and 0.6 mg./ml., and were dissolved in each pH buffer.
Results: Although a 26% increase in bladder capacity was recognized 1 hour after instillation of pH 8.44, 0.06 mg./ml. oxybutynin, no significant difference was found in comparison with control rats. At the concentration of 0.6 mg./ml., bladder capacity markedly decreased 30 minutes to 1 hour after instillation even at pH 6.44 and 8.44. Significant decreases in detrusor contraction pressure were recognized 30 minutes to 1 hour after instillation. However, there were no significant differences among the 3 pH oxybutynin solutions. Compared with preinstillation values, significant increases in residual urine rates were observed in all pH oxybutynin solutions. Furthermore, the residual urine rate after instillation of pH 8.44 oxybutynin solution differed significantly from that of pH 4.44 oxybutynin.
Conclusion: Our results demonstrate that pH and concentration of intravesical oxybutynin solution may play an important role in relaxation of the bladder. A high concentration of oxybutynin is considered irritating to the bladder mucosa.