This study aims to evaluate whether the use of alpha-blockers before flexible ureterorenolithotripsy facilitates the passage of the ureteral access sheath. The trial will enroll adult patients diagnosed with kidney stones who are scheduled for flexible ureteroscopy. Participants will be randomly assigned to receive or not receive alpha-blockers for seven days before surgery. The primary outcome is the rate of successful sheath placement without the need for a second procedure. Secondary outcomes include the incidence of ureteral injuries and the need for additional surgical interventions. The goal is to improve surgical efficiency and patient outcomes in the treatment of kidney stones.

Inclusion Criteria:

• Age ≥ 18 years
• Diagnosis of nephrolithiasis with surgical indication for flexible ureterorenolithotripsy
• Ability to provide written informed consent

Exclusion Criteria:

• Age < 18 years
• Pregnancy
• History of ureteral stricture, prior ureteral reconstructive surgery, and/or abdominal or pelvic radiotherapy
• Prior ureteroscopy or ipsilateral double-J stent placement within the past 3 months
• Chronic use of alpha-blockers for benign prostatic hyperplasia or medical expulsive therapy for ureteral stones