My urethral pain & spasms have eased with my increased Zanaflex dose (4mg twice a day), so I'm pretty sure my muscle spasms were the cause of that. I don't currently have a UTI and still get the occasional stabbing pain.
For what it is worth, I have had kidney stones and a couple large bladder stones (5/8" diameter!) over the last 18 months. I had procedures to remove them and once the bladder stone was out my frequency dropped! I can now sleep through the night and wake up dry. I've taken 20 mg of Oxybutinin for 30 years and it has worked fairly well but getting the large bladder stone out was the best help!