CAL: prescription diets

Question 1

What are therapeutic options for managing urolithiasis in dogs?

Answer 1

• reduce supersaturation of urine - change urine pH - UTIs if applicable - tx other conditions that increase the risk of urolithiasis

Question 2

Describe dietary management for struvite urolith

Answer 2

-general principles: decrease urine concentration, increase diuresis and water intake - calculolytic diets (dissolve crystals) - reduce urine concentration of urea, phsophorous and magnesium - moderate protein (to decrease urea for urease-producing bacteria), highly digestible, low fibre - use for 1 months beyond removal of struvite - not meant for long term - don’t forget AB tx for UTI

Question 3

What is supersaturation?

Answer 3

As the relative supersaturation (RSS) increases >1, the risk of urolith formation increases

Question 4

What to look for with UA?

Answer 4

whether there are detectable amounts of blood, protein, white blood cells, visible bacteria and to know the urine pH and specific gravity

Question 5

How to monitor struvite dietary management

Answer 5

persistence of CS, serial abdominal radiographs, urine pH, USG and evidence of crystals in urine.

Question 6

What emergency stabilisation is given for hyperkalaemia induced ECG abnormalities?

Answer 6

• Ca IV or administration of glucose and/or insulin - calcium gluconate = cardioprotective - insulin regulates K+ levels in blood (insulin –> reduces K+ in blood). Presumably giving glucose –> increased endogenous insulin –> reduces K+ in blood. - fluids containing glucose = help dilute the blood with non-K+ containing fluids

Question 7

Classic ECG signs with hyperkalaemia

Answer 7

• tented t waves - lack of p waves - QRS widening

Question 8

What is this type of crystal?

Answer 8

Crystals are v distinct and consistent with calcium oxalate dihydrate

Question 9

Prevention of reoccurence/tx of calcium oxalate dihydrate crystals

Answer 9

• diets promoting production of understaturation with calcium oxalate - avoid excess dietary calcium and oxalate - don’t restrict dietary phosphorous (i.e. don’t use low protein/renal diets) - manipulating urinary pH not helpful - specific prescription veterinary diets (some change pH, others increase diuresis and water intake) - manage any wt issues

Question 10

What is the reason so many Dalmations develop urate stones?

Answer 10

In most animals, the by-product of purine metabolism are converted first to hypoxanthine, then to xanthine, then uric acid and finally to allantoin. In affected Dalmations, the enzyme responsible for converting uric acid into allantoin has reduced activity, causing a build up of uric acid and leads to formation of urate uroliths.

Question 11

What are the nutritional strategies recommended for treating Dalmations with urate uroliths?

Answer 11

• Aimed at increasing urine pH and lower urine concentratons of uric acid, ammonium and/or hydrogen ions. • Calculolytic diets will also require a decrease in purine content – this requires severe protein restriction. • If commercial diets are not used, important ingredients to avoid include fish or offal. Alternate protein sources that are relative low in purines precursors include vegetable proteins, eggs and dairy products. • Other strategies such as switching to canned diets, and increasing diuresis via increasing salt content are also useful. • Protein restricted diets have an alkalinising effect on urine pH however sometimes it is still necessary to use alkalinising agents.

Question 12

Other than dietary manipulation, what else can be done to aid resolution of clinical disease in dalmations with uroliths?

Answer 12

• Like other uroliths, UTIs need to be appropriately treated. • In addition to diet, administering xanthine oxidase inhibitors (eg, allopurinol) can lower (most effectively) the concentration of uric acid in urine – however this will increase xanthine and hypoxanthine concentrations in urine and sometimes lead to xanthine urolith formation – in order to treat these, allopurinol use should be discontinued and a low purine-diet should be used

Question 13

What imaging is recommended for cystolith evaluation?

Answer 13

plain radiography usually adequate and sufficient

Question 14

What are these crystals?

Answer 14

cystine crystals (relatively uncommon versus other uroliths)

Question 15

Cause of cystine uroliths

Answer 15

an inborn error of metabolism characterised by a defective proximal tubular reabsorption of cystine and other amino acids. In dogs with this particular problem, only a small fraction of cystine is reabsorbed, leading to increased cystine excretion and urolith formation.

Question 16

Which factors impact the risk of cystine urolith formation?

Answer 16

• High concentration of cystine in urine • Decreased cystine solubility in urine with pH

Question 17

What is the strategy in managing dogs with cystine uroliths?

Answer 17

• Aim = reducing cystine in urine and this will require protein restriction in the diet. • Equally important would be to increase the solubility of cystine by alkalizing the diet. • Another strategy would be to add thiol-containing drugs to this dog’s regimen. Thiol-containing drugs react with cystine by a thiol-disulfide exchange reaction, resulting in the formation of a complex that is more soluble in urine than cystine. Such drugs include 2-MPG or N-(2-mercaptopropionyl)-glycine. This can dissolve cystine uroliths when combined with protein restriction and alkalinisation of urine.

Question 18

Outline tx strategy for cystine crystals

Answer 18

• Use a protein-restricted alkalinising diet • Increase urine volume (decrease urine specific gravity) • Alkalinisation of urine to pH > 7.4 • Administration of thiol-containing drugs

Question 19

What is this crystal?

Answer 19

Struvite