Page 746 - Small Animal Internal Medicine, 6th Edition

718 PART V Urinary Tract Disorders

BOX 43.2 act as inhibitors of CaOx urolith formation and therefore
should not be restricted in the diet. Dietary phosphorus
VetBooks.ir Guidelines for Increasing Dietary Moisture should not be excessively restricted because it could lead
to increased activation of vitamin D 3 to calcitriol by
1. Try feeding the canned formulation of the desired diet
if possible. 1α-hydroxylase in the kidney under the action of parathy-
roid hormone (PTH) and result in increased intestinal
• Feeding a high-moisture diet (>75% moisture) is absorption of calcium. Finally, dietary fats have been specu-
ideal. Canned formulations of diets are the easiest
way to achieve this in some animals. lated to be involved in CaOx stone formation in rats and
• Providing a choice of canned and dry foods for humans. Although the pathogenesis of spontaneous CaOx
cats is recommended because an abrupt change in stone formation in animals may differ, it may be prudent to
diet is usually not well tolerated. feed animals with hypertriglyceridemia a diet restricted in
2. If this is not practical, begin adding water to the dry fat (<2 g/100-kcal diet). When choosing a diet, the animal’s
diet: entire history, physical examination (including body condi-
• Begin with 1 cup of water/cup of dry food. tion score), and medical conditions need to be considered.
• Gradually increase the water content over 3-4 Drug therapy
weeks. If dietary manipulations alone are unsuccessful in pre-
• Ideally, 3-4 cups of water/cup of dry food is venting CaOx urolith recurrence, drug therapy may provide
recommended (≈70% moisture). additional benefit. The administration of hydrochlorothia-
• Evaluate the urine specific gravity (USG) and urine
sediment periodically; free-catch urine collected in zide (2 mg/kg orally [PO] q12h for dogs; 1 mg/kg PO q12h
the home environment is ideal for this. for cats) can be attempted because this may decrease urinary
3. Adjust moisture intake or consider the addition of salt calcium excretion. Serum calcium concentration should be
if necessary. evaluated shortly after beginning this agent to ensure that
hypercalcemia does not occur. Although there are no studies
about the efficacy of hydrochlorothiazide in cats with CaOx
stones, reports have suggested that this dosage is well toler-
need to be addressed concurrently. After using strategies ated and reduces the relative supersaturation of CaOx in
to increase the moisture content of the diet, if the urine is healthy cats. Also, citrate as potassium citrate (50-75 mg/kg
still too concentrated or the urine sediment findings remain PO q12h for cats or dogs) may be helpful because the citrate
abnormal, one can try the addition of sodium chloride (table can complex with calcium, thereby decreasing the urinary
salt) to the diet to increase the urine volume produced daily, concentration of CaOx and alkalinizing the urine.
unless the patients are hypertensive or have cardiovascu-
lar problems or renal disease. Feeding higher-sodium diets Struvite Stone Management
(>375 mg/100 kcal) dry foods should not a substitute for For dogs
feeding a high moisture food but can be considered in dogs Struvite uroliths occur more commonly in female dogs
and cats where urine dilution is not achieved and recurrence compared with male dogs. They are usually larger than CaOx
of CaOx is of concern. and often smooth in shape (Fig. 43.9). In dogs, unlike cats,
There are several diets marketed for CaOx prevention in almost all struvite calculi are infection-induced, usually by
cats and dogs, but studies on their efficacy are limited. Staphylococcus intermedius or, less commonly, by Proteus
Home-cooked diets can also be an option for some dogs and mirabilis. These bacteria have the ability to hydrolyze urea to
cats, particularly those with multiple comorbid conditions form ammonia and carbon dioxide. This reaction increases
that need to be managed concurrently. A consultation with the urine pH and makes ammonium available to form mag-
a veterinary nutritionist is recommend in these cases, and nesium ammonium phosphate crystals. Occasionally the
the readers are encouraged to consult with nutritionists for urine can be supersaturated with the minerals that comprise
the most up-to-date marketed diets for stone prevention. struvite uroliths, and stone formation can occur without an
Diets for CaOx prevention should not be restricted in infection present. If a urine culture is negative in a dog with
calcium, because this could increase the absorption of intes- struvite uroliths, the stone and/or bladder mucosa can also
tinal oxalate. Excess calcium and oxalate intake should also be cultured to be certain that a bacterial pathogen is not
be avoided. High-moisture, lower-calorie, low-oxalate treats present. Dissolution of canine struvite uroliths can be done
can also be a good option for owners who wish to provide in the same manner as described for cats (see later), but
treats for their pet (see www.ohf.org/docs/Oxalate2008.pdf proper antimicrobials, based on minimum inhibitory con-
for approximate oxalate contents of many human foods). The centration (MIC) testing results, should also be adminis-
list can be reviewed with the client, and foods such as raisins, tered. By convention, these antimicrobials have been
grapes, and other toxic foods listed that are contraindicated administered throughout the duration of the dissolution
for pets should be discussed with the owner. protocol. No studies have been performed to see if this dura-
Other nutrients to consider in the dietary management tion of antimicrobial therapy is warranted, and shorter
of CaOx urolithiasis include magnesium and phosphorus. courses may be considered. Three diets are currently mar-
Urinary magnesium, phosphate, and citrate are thought to keted for struvite dissolution in dogs (Royal Canin Canine