Feline Magnesium Ammonium Phosphate (Struvite) Uroliths

In most cats, magnesium ammonium phosphate hexahydrate (struvite) uroliths form in sterile urine and may be affected by several dietary factors. Infection-induced struvite uroliths can occur in cats as a sequela to urinary tract infections with urease producing microbes. Feline STERILE Struvite Uroliths Urolith Dissolution Prior to attempting dissolution, perform diagnostic studies to identify urolith size and location, as well as confirmation of urolith composition (urinalysis, radiography, analysis of retrieved stones, etc.). Initiate therapy with calculolytic diet that promotes acidic urine, promotes diuresis, and is restricted in phosphorus and magnesium. Monitor response to therapy at appropriate intervals (every 2 to 4 weeks). Uroliths dissolved in an average of 4 weeks in cats with sterile struvite uroliths fed a struvitolytic diet. Minimizing Urolith Recurrence Encourage additional water consumption or feed a canned diet to promote diuresis. Feed a maintenance diet that is restricted in magnesium and phosphorus and promotes acidic urine. Use appropriate caution in cats predisposed to calcium oxalate urolithiasis. Feline INFECTION-INDUCED Struvite Uroliths Urolith Dissolution Prior to attempting dissolution perform diagnostic studies to identify urolith size and location, as well as confirmation of urolith composition (urinalysis, radiography, analysis of retrieved stones, etc.). Perform urine culture and susceptibility to identify bacterial pathogens (if present), and select appropriate antimicrobial therapy. Initiate therapy with calculolytic diet that promotes acidic urine, promotes diuresis, and is restricted in phosphorus and magnesium. Administer appropriate antimicrobial agent; continue until there is radiographic evidence of complete dissolution. Monitor response to therapy at appropriate intervals (every 2 to 4 weeks). Uroliths dissolved in an average of 11 weeks in cats with infection-induced struvite uroliths fed a struvitolytic diet in addition to appropriate antimicrobics. Minimizing Urolith Recurrence Perform appropriate diagnostic studies to eradicate or control bacterial urinary tract infections. Infection-induced struvite uroliths will not form in the absence of urease-positive microbial infections. Early detection of small uroliths that recur despite appropriate medical therapy facilitates non-surgical removal by voiding urohydropropulsion. Uroliths removed by voiding urohydropropulsion should be quantitatively analyzed.  All prevention recommendations should be adjusted to meet individual patient's needs. We recommend follow-up urinalyses, serum chemistry profiles, and radiographs on a periodic basis. Further references: Lulich JP, Osborne CA, Unger LK, et al: Nonsurgical removal of urocystoliths by voiding urohydropropulsion. In Journal of the American Veterinary Medical Association. Vol 203, pp. 660-663, 1993 Osborne, CA, et al.: Diagnosis, Medical Treatment, and Prognosis of Feline Urolithiasis, The Veterinary Clinics of North America, Small Animal Practice, 26:589-627, 1996 Allen, Timothy A., Kruger, John M., Feline Lower Urinary Tract Disease. Small Animal Clinical Nutrition 4th ed., 2000, pp. 689-723