The objective of this study was to determine the efficacy of feeding the commercially available diet, Purina Pro Plan Veterinary Diets UR Urinary St/Ox, for the dissolution of struvite cystoliths in cats with naturally occurring disease. Twelve cats with clinical signs of lower urinary tract disease and cystoliths confirmed via radiographs were enrolled. The cats were fed the study diet ad libitum and assessed by abdominal radiographs weekly. Cats with cystoliths that resolved based on radiographs and confirmatory ultrasound examination were considered diet successes. Cats with no change in cystolith size after 2-6 weeks underwent cystotomy for stone removal, aerobic culture and antimicrobial susceptibility testing, and analysis. All cats accepted the study diet, and weight loss was not noted over the course of the study. Total cystolith dissolution was achieved by week 2 for 5 cats, which were presumed to have struvite cystoliths. All other cats underwent cystotomy for stone removal after radiographic evidence of cystoliths were still present at 2 weeks (1 cat with severe signs), 4 weeks (5 cats), or 6 weeks (1 cat). The cystoliths that were surgically removed were calcium oxalate (5 cats) and mixed (2 cats) and would not be expected to dissolve with this diet. Follow-up radiographs from 6 cats fed the diet long term (3 presumed struvite and 3 with other cystoliths removed surgically) were collected from 1 to 6 months after beginning the study and showed no evidence of cystolith recurrence.
While larger case numbers are needed, these results suggest that feeding Purina Pro Plan Veterinary Diets UR Urinary St/Ox can successfully dissolve cystoliths that are likely struvite and may lessen the risk of recurrence of struvite and calcium oxalate cystoliths.