A 68-year-old man presents with lower urinary tract symptoms (LUTS) including nocturia (×4 per night), weak urinary stream, and hesitancy for 8 months. Digital rectal examination reveals a smooth, firm, symmetrically enlarged prostate. Post-void residual urine is 45 mL. Uroflowmetry shows a peak flow of 8 mL/s. He has no history of acute urinary retention or recurrent UTIs. What is the drug of choice for initial medical management?