This multicenter randomized controlled trial will evaluate whether preoperative tamsulosin, intraureteral aminophylline, or their combination can improve ureteral access during primary retrograde intrarenal surgery for renal stones. Adult patients with unilateral renal stones measuring 2 cm or less and planned placement of a 10/12 Fr ureteral access sheath will be randomly assigned to one of four groups in a 2x2 factorial design. Participants will receive either tamsulosin or placebo for 7 days before surgery and either intraureteral aminophylline or intraureteral placebo during the procedure. The main outcome will be successful first-attempt placement of the planned 10/12 Fr ureteral access sheath after study solution instillation, without active ureteral dilatation, sheath downsizing, prestenting with deferred surgery, or abandonment of the procedure due to access failure.

Retrograde intrarenal surgery is a commonly used minimally invasive procedure for the treatment of renal stones. Successful completion of the procedure may require placement of a ureteral access sheath. However, ureteral access sheath insertion can be difficult in some patients because of ureteral resistance or spasm, which may lead to ureteral trauma, active ureteral dilatation, prestenting with delayed surgery, or inability to complete the planned procedure.

This study is designed to compare systemic, local, and combined pharmacologic strategies for facilitating ureteral access during primary retrograde intrarenal surgery. Tamsulosin is an alpha-1 adrenergic receptor blocker that may reduce ureteral tone when given before surgery. Aminophylline is a smooth-muscle relaxant that may reduce ureteral spasm when administered locally into the ureter during the procedure.

This is a prospective, multicenter, randomized, double-blind, placebo-controlled, parallel-group trial with a 2x2 factorial design. Eligible adult patients with unilateral renal stones measuring 2 cm or less who are scheduled for primary retrograde intrarenal surgery with planned 10/12 Fr ureteral access sheath placement will be randomized in a 1:1:1:1 ratio. The four treatment combinations are: placebo capsule plus intraureteral placebo, tamsulosin capsule plus intraureteral placebo, placebo capsule plus intraureteral aminophylline, and tamsulosin capsule plus intraureteral aminophylline.

Patients assigned to tamsulosin will receive tamsulosin 0.4 mg once daily for 7 days before surgery, while patients assigned to placebo will receive a matching placebo capsule. During surgery, the assigned intraureteral solution will be instilled through an open-end ureteric catheter positioned in the distal ureter on the study side. After a standardized 5-minute waiting period, one controlled attempt will be made to place the planned 10/12 Fr ureteral access sheath.

The primary endpoint is successful first-attempt placement of the planned 10/12 Fr ureteral access sheath after study solution instillation, without active ureteral dilatation, sheath downsizing, prestenting with deferred retrograde intrarenal surgery, or abandonment of the procedure due to access failure. If the planned sheath cannot be inserted safely, management will proceed according to a predefined rescue pathway, including active ureteral dilatation if considered safe or ureteral stenting with deferred surgery. Forced sheath advancement against marked resistance will be avoided.

Secondary outcomes will assess flexible ureteroscope advancement, need for rescue maneuvers, access-related ureteral injury, operative outcomes, postoperative pain, complications, hospital stay, and stone-free status during follow-up.

Inclusion Criteria:

• Age 18 years or older.
• Unilateral renal stone 2 cm or less in maximal diameter on preoperative imaging.
• Scheduled for primary retrograde intrarenal surgery.
• Ability to provide written informed consent.

Exclusion Criteria:

• Prior ureteral stenting on the study side.
• Bilateral same-session retrograde intrarenal surgery.
• Concomitant ureteral stone requiring primary semirigid ureteroscopy as the main procedure.
• Known ureteral stricture or prior ureteral reconstructive surgery on the study side.
• Active urinary tract infection or untreated positive urine culture.
• Pregnancy.
• Known allergy or contraindication to tamsulosin or aminophylline.
• Significant cardiac arrhythmia, uncontrolled ischemic heart disease, seizure disorder, or hyperthyroidism.
• Severe hepatic impairment.
• Inability to comply with the 7-day preoperative medication protocol.

Individual participant data will not be shared because the study involves individual-level clinical and operative data from a multicenter interventional trial. Only aggregated, de-identified study results will be reported in publications. Any future data sharing request will require approval from the Research Ethics Committee, Faculty of Medicine, Beni-Suef University, and the participating study centers.

Preoperative capsules will be identical in appearance, packaging, and labeling. Intraureteral study solutions will be prepared in identical syringes of equal volume by personnel not involved in surgery, postoperative assessment, or data analysis. Participants, care providers, investigators, and outcome assessors will remain blinded to treatment allocation whenever feasible.