Intravesical Aminophylline to Facilitate Ureteroscopic Access in Children With Distal Ureteral Stones.

This study will evaluate whether intravesical aminophylline can facilitate semi-rigid ureteroscopic access in children with distal ureteral stones when the first gentle attempt to enter the ureter is unsuccessful. Children scheduled for semi-rigid ureteroscopy for distal ureteral stones will first undergo the standard gentle attempt to pass the ureteroscope through the ureteric orifice and intramural ureter. If access is achieved, the child will continue standard treatment and will not be randomized. If access is not achieved, the child will be randomized during the operation to receive either intravesical aminophylline or intravesical normal saline placebo. The study solution will be instilled into the bladder for approximately 5 minutes, then drained, and a second gentle ureteroscopic access attempt will be made. The main outcome is successful same-session passage of the intended semi-rigid ureteroscope without balloon dilation. The study will also assess the need for JJ stenting and deferred ureteroscopy, same-session stone treatment, operative outcomes, complications, and early aminophylline-related safety.