What is the first-line medical expulsive therapy for distal ureteral stones and its mechanism?

• A. Naproxen; NSAID for pain.
• B. Tamsulosin; alpha-1 blocker that relaxes ureteral smooth muscle to aid passage.
• C. Nifedipine; calcium channel blocker
• D. Morphine; analgesic

Answer: (B)

First-line medical expulsive therapy for distal ureteral stones is an alpha-1 adrenergic blocker that relaxes the ureteral smooth muscle to aid passage. Tamsulosin does this by blocking alpha-1 receptors in the distal ureter, especially the alpha-1D subtype that’s prevalent there. With the smooth muscle relaxed, ureteral tone and spasm decrease, so the stone has an easier path to move down into the bladder. This intervention often shortens the time to passage and can reduce the need for surgical intervention, while allowing continued movement of urine and relief of painful spasms. Other options mainly address pain (an NSAID or an opioid) or have less strong evidence for actively promoting stone passage (calcium channel blockers like nifedipine), so they’re not considered first-line for expulsion.