Page 359 - Feline Cardiology

374 Section L: Comorbidities

have impacts on the other. Specifically, diets for cats with a dilute urine (Westropp and Buffington 2010). Urinary
lower urinary tract disease have historically been formu- dilution is theorized to be beneficial by decreasing the
lated to contain limited quantities of magnesium. Based concentration of solutes (which could otherwise pre-
on the experimental cardiomyopathies produced by cipitate and allow formation of a urethral plug and/or
hypomagnesemia in rats and dogs (Freeman et al. 1997), uroliths), increasing the frequency of elimination and
and the hypomagnesemia that can occur either with reducing the concentration of caustic substances in
urinary acidification or with diuretic usage (Freeman contact with the bladder mucosa. One time-honored
et al. 1997), an association has been suggested between method adopted for this effect has been to increase a
hypomagnesemia and feline heart disease. This associa- food’s sodium content in order to trigger thirst and
tion has been investigated and was not supported. greater water consumption. Because this sequence
Retrospective analysis has identified that a majority of occurs via an increase in circulating blood volume, such
cats (40/45, 89% in one study) (Freeman et al. 1997) an approach would not be recommended for a cat with
with HCM are fed a low-magnesium diet, perhaps concurrent heart disease. Modern diets designed and
similar to the cat population at large. Yet a study com- marketed for urolith prevention are variable in their
paring 10 cats with HCM to 10 healthy control cats sodium content compared to the equivalent mainte-
demonstrated no difference in serum creatinine concen- nance diet (Table 24.2). For example, a diet designed to
tration, serum magnesium concentration, or urinary reduce the risk of urolith formation, Purina UR Urinary
magnesium excretion, suggesting that in the cat, HCM St/Ox Feline dry kibble, contains 1.17% sodium on a dry
is not associated with an alteration in magnesium matter basis (DMB), while a nonprescription diet with
balance (Freeman et al. 1997). Another study identified similar indications, Purina ProPlan Urinary Tract Health
no benefit to magnesium supplementation: 15 cats Formula feline kibble, contains 0.26% sodium DMB; the
with HCM who received placebo PO q 24h for 12 latter compares favorably with 0.20% sodium DMB in
weeks showed no difference in magnesium status or the same company’s feline cardiovascular diet kibble
echocardiographic parameters compared to 15 cats that (Purina CV) whereas the former compares poorly
received 210 mg MgCl (providing 25 mg elemental Mg) (Purina Guide 2010). A typical maintenance diet (e.g.,
PO q 24 for 12 weeks (Freeman et al. 1997). Based on Purina ProPlan Chicken & Rice or Salmon & Rice feline
this limited but objective evidence, magnesium- kibble) contains 0.53–0.81% sodium DMB. Finally,
restricted diets appear to be fed routinely to cats with feline diets also vary in sodium content when the canned
heart disease without deleterious cardiovascular effects. formulation is compared to the dry kibble formulation.
Routine supplementation with dietary magnesium, or For example, the canned formulation of Purina UR
Urinary St/Ox Feline diet contains approximately half as
avoidance of magnesium-restricted diets when manag-
Comorbidities ing cats with concurrent heart disease and lower urinary much sodium (0.62%) on a DMB as its kibble counter-
part (1.17%), whereas canned formulations with gravy
tract disease, appears unjustified.
often have the reverse profile: Purina ProPlan Salmon &
One of the cornerstones of preventing recurrence of
Rice Entrée contains 1.47% sodium DMB compared to
feline lower urinary tract disease is the maintenance of

Table 24.2. Sodium content of diets designed for cats with recurrent lower urinary tract signs

Diet—Dry Kibble [Na] DMB Diet—Wet Canned [Na] DMB

Hills c/d multicare 0.35% Hills c/d multicare—seafood 0.33%
Hills c/d multicare—chicken 0.33% Hills c/d multicare—chicken 0.32%
Hills s/d 0.40% Hills s/d 0.37%
Iams low pH/S 0.49% Iams low pH/S 0.43%
Iams mod pH/O 0.49% Iams mod pH/O 0.43%
Purina UR St/Ox 1.17% Purina UR St/Ox 0.62%
Waltham S/O control pH 1.4% Waltham S/O control pH 1.05%

DMB = dry matter basis.
Sources: Purina Veterinary Diets: Purina Veterinary Product Guide, VET 0866H-0110; January 2010; www.walthamusa.com/
newDiets.html; www.hillspet.com/products.html; www.iams.com. Websites accessed 6/23/10. Additional information provided
courtesy of Dr. Sarah Miller, Cube Route Pty (Ltd).