I have been taking Allopurinol (4 100mg tablets/day) for over 8 years to prevent recurrence of gout.  This medication has not had any affect on my pouch.

The only thing that I can suggest to help prevent kidney stones is to cut back on drinking tea and eating chocolate, both of these items containing oxalate which binds to calcium and forms stones.

I was diagnosed once with little crystal not exactly stones though. The doctor asked if I could drink alot of beer to clear it up and I did. Its funny coz I'd drink 2-3 bottles just to pee hard enough to get those crystals out of me. I did this 3-4 times. On my next visit I was clear of stones. But my doctor told me it wasnt permanent solution and asked me to increase my fluid intake to prevent stones in future. Also he asked me to stay away from spinach, beetroot and tomatoes , though I still eat both of them. I just drink 4-5 lts water minimum in a day now.