Acute urinary retention is a common emergency in men with benign prostatic hyperplasia. After bladder drainage with a urethral catheter, patients usually undergo a trial without catheter to determine whether they can pass urine again without recatheterization.

This study will evaluate whether adding tadalafil 5 mg once daily to tamsulosin 0.4 mg once daily improves the chance of successful trial without catheter in men with first-episode acute urinary retention due to presumed benign prostatic hyperplasia.

Participants will be randomly assigned to receive either tamsulosin plus tadalafil or tamsulosin plus a matching placebo. Study medication will start within 24 hours after catheterization. The catheter will be removed on Day 7. If the first trial without catheter fails, the catheter will be reinserted and a second rescue trial without catheter will be performed on Day 14.

The main outcome is overall catheter-free success by Day 14. Participants will also be followed for recurrent urinary retention, post-void residual urine, urinary flow, catheter-related complications, drug-related adverse events, and the need for benign prostatic hyperplasia-related surgery within 3 months.

Inclusion Criteria:

• Male patient aged 50 years or older.
• First episode of spontaneous painful acute urinary retention.
• Successful urethral catheterization at presentation.
• Drained urine volume at presentation of at least 300 mL.
• Clinical impression of benign prostatic obstruction or benign prostatic hyperplasia based on history, digital rectal examination, and/or ultrasound evidence of enlarged prostate.
• Ability to provide written informed consent.

Exclusion Criteria:

• Previous episode of acute urinary retention.
• Chronic painless urinary retention phenotype.
• Active urinary tract infection or sepsis.
• Gross hematuria with clot retention.
• Suspected or known urethral stricture.
• Neurogenic bladder or major neurologic disease affecting voiding.
• History of prostate cancer or bladder cancer.
• Previous prostate surgery.
• Current use of nitrates or guanylate cyclase stimulators.
• Contraindication to tadalafil or tamsulosin.
• Severe hypotension or unstable cardiovascular disease.
• Severe renal impairment.
• Severe hepatic impairment.
• Current or recent use of phosphodiesterase type 5 inhibitors before enrollment.

Individual participant data will not be shared publicly because the study includes individual-level urological and treatment-related clinical data, and participant-level data sharing is not currently included in the ethics approval or informed consent. Only aggregated, de-identified results will be reported in publications or presentations. Any future sharing of de-identified participant-level data would require additional approval from the Research Ethics Committee, Faculty of Medicine, Beni-Suef University, and an appropriate data-sharing agreement.

All participants will receive open-label tamsulosin 0.4 mg once daily. Participants will be randomized to receive either tadalafil 5 mg once daily or a matching placebo once daily. Tadalafil and placebo tablets will be identical in appearance, packaging, and labeling. Participants, treating physicians, investigators, study coordinators, outcome assessors, and data analysts will remain blinded to tadalafil/placebo allocation. Emergency unblinding will be permitted only when knowledge of treatment allocation is essential for participant safety.