These are a couple of sources for hints about how to remove stains from clothes:
There is a lot of information about how to remove urine stains from mattresses, for example this is a good one:
As A Last Resort
I read somewhere in the web that there is a pet urine stain removal liquid that will remove urine stains off of anything. It is called Nature's Miracle.
- If none of this works, then I would say, throw the garment out and buy new ones. It is sad to lose a practically new underwear to a urine stain but if you must, you must.