Purina Pro Plan Veterinary Diets UR St/Ox Urinary is a nutritionally complete diet that has been specially developed to help dissolve struvite urinary crystals and stones. Designed to reduce the risk of urinary stones recurring (struvite and calcium oxalate), Purina UR will also help to nutritionally manage feline idiopathic cystitis by increasing water intake and encouraging the production of dilute urine.