Veterinary Medicine - October 2008 - (Page 553)

Prevention* • Infectious: Monitor for bacterial infection and treat as needed • Sterile: Feed a diet formulated for struvite prevention Comments • One of the two most common urolith types in dogs and cats • Infection-related struvite formation is associated with urease-producing bacteria. • Resolve or ameliorate hypercalcemia, if present, by using the appropriate treatment for the underlying cause, if possible. • Feed a diet formulated for preventing oxalate calculi or a high-ﬁber diet and potassium citrate. • Thiazide diuretics (contraindicated in hypercalcemic patients) • Dogs: Feed a low-purine diet formulated for urate calculi management with or without allopurinol. • Cats: Feed a diet formulated for managing kidney disease. • Correct portosystemic shunt, if present. Feed a protein-restricted, alkalinizing diet. One of the two most common urolith types in dogs and cats Most struvite uroliths in dogs are caused by a urinary tract infection, occur predominantly in females, and have a breed predisposition for miniature schnauzers, Shih Tzus, bichon frises, miniature poodles, cocker spaniels, and Lhasa apsos.24 Most struvite uroliths in cats are sterile and not associated with a known sex predisposition. Cat breeds predisposed to struvite formation include the foreign shorthair, Ragdoll, Chartreux, Oriental shorthair, domestic shorthaired cat, and Himalayan.25 The age predisposition for sterile struvite urolith formation in cats is between 1 and 10 years old with the incidence decreasing after about 7 years of age. Sterile struvite uroliths may be associated with increased to normal magnesium concentrations in the diet, but it is still unclear whether magnesium triggers struvite urolith formation.13,14 Alkaluria and low urine volume also appear to put cats at risk for developing sterile struvite uroliths. Infection-related struvite uroliths occur as a result of an underlying urinary tract infection. The bacteria involved are most commonly urease-producing Staphylococcus species, although urease-producing Proteus species and, rarely, ureaplasma organisms may also be involved.24 Occasionally, other bacteria are cultured from affected patients. The breakdown of urea by the bacteria releases ammonia into the urine, increasing the pH and availability of ammonium and phosphate ions, all of which predispose a patient to struvite urolith formation. Third most common urolith composition in dogs and cats Recognized more recently in cats but has been reported in Cavalier King Charles spaniels, dachshunds, and dogs receiving allopurinol Treatment. Feeding a calculolytic diet (Table 1) can dissolve both sterile and infection-related struvite urocystoliths and nephroliths by creating an acidic, dilute urine undersaturated with magnesium, ammonium, and phosphorus.24-27 The dissolution time for uroliths varies, but it averages about two to three months for infection-related uroliths and three to six weeks for sterile uroliths.24-26 Dissolution of infection-related struvite uroliths occurs more rapidly if an appropriate antibiotic is administered concurrently. Antibiotic therapy is best determined by bacterial culture and antimicrobial sensitivity testing of urine obtained by cystocentesis. Ideally, a urine culture should be performed before antibiotics are initiated and periodically during the dissolution process. By evaluating serial urinalyses and abdominal radiography or ultrasonography every four weeks, dissolution therapy can be altered as needed for individual patients. Urinalysis ndings compatible with an ongoing infection (bacteriuria, pyuria, alkaluria) indicate a need to reassess antibiotic therapy through urine bacterial culture and antimicrobial sensitivity testing. Diagnostic imaging is the primary means of determining the success of the dissolution therapy. Continue the calculolytic diet and antibiotic administration for one month after complete dissolution of uroliths as established by imaging.19,24,25 A calculolytic diet is not a maintenance diet. For example, according to the manufacturer’s product guide (2005 Hill’s Key to Clinical Nutrition), Prescription Diet s/d feline and canine (Hill’s VETERINARY MEDICINE October 2008 553

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Veterinary Medicine - October 2008 Contents Leading Off Clinical Exposures Idea Exchange Stalking Stones Vaginitis in Dogs CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - October 2008

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