Veterinary Medicine - October 2008 - (Page 556)

Urolithiasis PEER-REVIEWED 4A. A ventrodorsal abdominal radiograph of a 7-year-old, castrated male basset hound reveals a large radiopaque nephrolith conforming to the shape of the left renal pelvis. 4C. The same nephrolith seen in Figures 4B. The same nephrolith seen in Figure 4A and 4B, exposed after nephrectomy. The composition of the body of the nephrolith was 95% magnesium ammonium phosphate hexahydrate and 5% calcium phosphate and of the shell was 80% magnesium ammonium phosphate hexahydrate and 20% calcium phosphate. 4A as seen during the nephrogram stage of an excretory urogram. Note the remnant of the left renal pelvis seen as a dark zone adjacent to the nephrolith. and urine alkalinization are recommended.31 Diets formulated for oxalate urolith prevention in dogs and cats are listed in Table 1. In addition, in dogs Prescription Diet Canine w/d and potassium citrate (e.g. Urocit-K—Mission Pharmacal, 75 mg/ kg orally twice a day) are also options, especially in obese patients or those prone to developing pancreatitis.24 And in some hypercalcemic cats with calcium oxalate uroliths, Prescription Diet Feline w/d (Hill’s Pet Nutrition) and potassium citrate (75 mg/kg orally twice a day) normalizes calcium concentrations.34,35 In people, potassium citrate’s alkalinizing effect helps decrease bone calcium release and promote calcium excretion in a more soluble form, calcium citrate.24,25 These same bene cial effects may occur with potassium citrate administration in dogs and cats. The desired urine pH range for preventing calcium oxalate urolith formation is 6.5 to 7.5. If diet or diet plus potassium citrate fails to prevent calcium oxalate urolith recurrence, consider adding thiazide diuretics (hydrochlorothiazide 2 to 4 mg/kg orally twice a day)33 to decrease the calcium excretion in the urine.36,37 Although unproven in cats, thiazide diuretics decrease urinary calcium excretion in people and dogs with calcium oxalate urolithiasis. A study in dogs indicated that feeding them Prescription Diet u/d (Hill’s Pet Nutrition) in conjunction with hydrochlorothiazide administration enhanced reduction of urine calcium.36 Thiazide diuretics are contraindicated in hypercalcemic patients because they may aggravate the hypercalcemia. Use loop diuretics, such as furosemide, with caution in patients at risk for calcium oxalate urolithiasis since their mechanism of action may increase the formation of such uroliths by augmenting calcium urine excretion. Avoid supplementation of vitamin C, an oxalate precursor, and vitamin D, an aid to the gastrointestinal absorption of calcium, in patients with calcium oxalate urolithiasis.31 cats is purine. Most purine uroliths are composed of urates (uric acid and uric acid salts).24,34 Unlike struvite and calcium oxalate uroliths, urate uroliths have varied relatively little in incidence over the last 20 years, accounting for about 4.6% of uroliths in cats and 8% in dogs.14,22 Characteristics. Ammonium urate crystals are large and irregular in shape, and uric acid crystals are slender and hexagonal. These crystals form small; smooth; round; light-yellow, light-brown, or light-green radiolucent uroliths that are found most frequently in the bladder or urethra. Positive or double-contrast cystography or urethrography or highfrequency ultrasonography is usually needed for detection.24,39 Dalmatians and English bulldogs are the classic breeds associated with this urolith because of inherent differences in the way that uric acid is metabolized and transported in these dogs. Male Dalmatians and English bulldogs are affected more commonly than females. Dalmatians are thought to have impaired Urate (purine) The third most common noncompound type of urolith reported in dogs and 556 October 2008 VETERINARY MEDICINE

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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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