Tanya

 

TANYA'S

COMPREHENSIVE GUIDE TO

FELINE CHRONIC KIDNEY DISEASE

 

 

 

TREATMENTS FOR PHOSPHORUS AND CALCIUM IMBALANCES AND

 

SECONDARY HYPERPARATHYROIDISM, INCLUDING CALCITRIOL

 

ON THIS PAGE:


Phosphorus Imbalances


Calcium Imbalances


Secondary Hyperparathyroidism, Including Calcitriol and Cinacalcet (Sensipar)


 

 

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Home > Treatments > Phosphorus, Calcium and Secondary Hyperparathyroidism

 


Overview


  • Imbalances of phosphorus and calcium levels within the body are very common in CKD cats.

  • Eventually these imbalances can lead to a serious condition known as secondary hyperparathyroidism.

  • This page discusses the control of phosphorus and calcium levels in order to reduce the risk of secondary hyperparathyroidism.

  • It also discusses treatments which may be used if secondary hyperparathyroidism is present.

  • Please see Diagnosis for more information on these issues.


Phosphorus Imbalances


 

Low Phosphorus Levels (Hypophosphataemia)


Low phosphorus levels (below 3 mg/dl or 1.0 mmol/L) are extremely uncommon in CKD cats, though are occasionally seen in diabetic cats on insulin, or in cats with certain kinds of cancer. They may also be seen in a cat who is being fed following a prolonged period of starvation.

 

If the phosphorus level is too low as a result of using phosphorus binders, you can reduce the dose of binder which you are giving. If you think there is a different cause, speak to you vet.

 

See Diagnosis for more information on low phosphorus levels.

 

High Phosphorus Levels (Hyperphosphataemia)


In most cases, CKD cats have high phosphorus levels. High phosphorus levels can make the cat feel bad and may make the CKD progress faster. For a CKD cat, being within the normal range is not sufficient.

 

If your cat's phosphorus level is over 6 mg/dl (USA) or 1.9 mmol/L (international), it is too high and you need to get it under control.

 

This important topic has its own page here.

 


Calcium Imbalances


 

Since phosphorus and calcium work together in the body, calcium imbalances are also relatively common in  CKD cats. High calcium levels (hypercalcaemia) are more common in CKD cats, but some cats have low calcium levels (hypocalcaemia).

 

Managing calcium disorders (2014) Odunayo A Clinician's Brief Jun 2014 pp77-80 has more information about how to handle calcium imbalances.


Low Calcium Levels (Hypocalcaemia)


 

Although high calcium levels are more common in CKD cats, low calcium levels are occasionally seen.

 

The simplest treatment is a calcium supplement such as calcium carbonate (e.g. Tums, or an over the counter calcium carbonate product). If this type of treatment is used, calcium blood levels should be checked regularly because the opposite problem of high calcium may result.

 

Calcitriol is a hormone produced by the kidneys which helps to regulate parathyroid hormone (PTH), so some people use calcitriol as a supplement to try to control secondary hyperparathyroidism. Since calcitriol tends to increase calcium levels, occasionally it is also used for cats with low calcium levels. In such cases, it would normally be dosed twice daily in extremely tiny doses. See below for more information on calcitriol.

 

Dr Larry Nagode, formerly of Ohio State University College of Veterinary Medicine, has stated that niacin and niacinamide (vitamin B3), which some people are now using as phosphorus binders, may increase calcium levels and therefore might be a suitable supplement for cats with low calcium levels. I do not know what might be an acceptable dose when used for this purpose.

 

In really severe cases, intravenous calcium may be necessary at the vet's office, though  fortunately this is rare. Parenteral calcium for hypocalcemia: different salts, different dosages (2015) Plumb DC Plumb's Therapeutic Brief Sept 2015 has more information about this.

 


High Calcium Levels (Hypercalcaemia)


 

High calcium levels are more common in CKD cats than low calcium levels, but it is not always essential to treat hypercalcaemia.

 

See Diagnosis for more information on hypercalcaemia.

 

High Calcium Levels: When to Treat


High calcium levels are not normally a problem unless:

  1. ionised calcium levels are also high. If ionised calcium levels are high, you definitely need to take action; or

  1. calcium multiplied by phosphorus is higher than 60-70 in US values or 5 in international values. This increases the risk of calcification, so you should ask your vet about trying to control total calcium levels. (This also applies if you multiply phosphorus by ionised calcium, and the level is higher than 8.75 in US values or 35 in international values).

High Calcium Levels: Treatments


High Calcium Levels: Simple Treatments


These treatments are simple in that you will probably be using them for other reasons anyway, or they do not require much effort to implement. You may well find that you need to use more than one treatment.

See below for more advanced treatments.'

 

High Calcium Levels: Metabolic Acidosis


Metabolic acidosis can contribute to hypercalcaemia, so if your cat has metabolic acidosis, treating it can help reduce calcium levels.

 

High Calcium Levels: Subcutaneous Fluids (Sub-Qs)


Keeping your cat properly hydrated is one of the main goals of CKD treatment, so most cats with creatinine over 3.5 mg/dl  or 300 µmo/L will be receiving sub-Qs for this reason. As it happens, giving sub-Qs may also reduce calcium levels, though it is not usually recommended to use sub-Qs solely in order to control calcium levels.

 

Normally cats on sub-Qs with high calcium levels are given saline solution rather than lactated ringers solution (LRS). This is for two reasons: firstly, saline solution has no added calcium, and secondly, saline solution promotes calcium excretion in the urine. Alternatively, Normosol-R might be suitable. If you are using LRS, discuss switching with your vet.

 

High Calcium Levels: Phosphorus Binders


Since phosphorus and calcium levels within the body are closely related, reducing elevated phosphorus levels may also help reduce calcium levels.

 

Even if your cat's calcium levels are normal, if your cat's phosphorus level is over 6 mg/dl or 1.9 mmol/L, you need to take steps to control it, see All About Phosphorus.

 

Never use calcium-based phosphorus binders in a cat with elevated calcium levels.

 

High Calcium Levels: Limit Treatments Containing Calcium or Vitamin D


Slippery elm bark contains calcium, so it is probably safer not to use it if your cat has hypercalcaemia.

 

Some people have found that using lactulose to control constipation has led to hypercalcaemia in their cats. This may be coincidence, since hypercalcaemia is not uncommon in CKD cats, but you may wish to avoid lactulose if your cat already has hypercalcaemia, and consider alternative treatments if your cat has developed hypercalcaemia since beginning lactulose. See All About Constipation for more information and alternative treatments for constipation.

 

Also check for any supplements containing Vitamin D, and ensure that you are not feeding a food high in Vitamin D.

 

High Calcium Levels: Dietary Changes


It is worth checking which food you are feeding because some contain more calcium than others.

 

The body needs a balance between phosphorus and calcium, so foods usually have a particular ratio of calcium to phosphorus. The minimum is 1:1, though for healthy cats a higher ratio of calcium to phosphorus is not normally a problem. Standard commercial diets tend to have a ratio of around 1.2:1 (calcium to phosphorus).

 

Therapeutic kidney diets tend to contain more calcium in ratio terms because they are usually focused on keeping phosphorus levels low:

  • Hill's k/d has a level of 1.7:1 canned and 1.43 dry;

  • Purina NF is 1.68:1 for the dry and 1.36:1 for the canned;

  • Royal Canin has much higher levels, at around 2:1;

but the overall amount of calcium is still usually low.

 

If your cat is hypercalcaemic and in IRIS stages 1 and 2, discuss with your vet whether to feed a normal commercial diet with a lower calcium content rather than a therapeutic kidney diet. Cats in these stages do not normally need a reduced protein diet, see Nutritional Requirements, though it must not be forgotten that a therapeutic kidney diet has many features other than reduced protein levels, see Which Foods. Your vet can help you decide what to focus on.

 

If your cat does require a therapeutic kidney diet, I would check the calcium:phosphorus ratio carefully and aim for a food with a lower calcium:phosphorus ratio, assuming your cat will eat it. You might wish to add a food to it which is relatively low in calcium, in order to adjust the calcium:phosphorus ratio. You should also avoid feeding acidified diets.

 

Nutritional management of idiopathic hypercalcaemia in cats (2012) Peterson ME Insights into Veterinary Endocrinology discusses ways to treat idiopathic hypercalcaemia (idiopathic means no obvious cause can be found) through diet.

 

High Calcium Levels: Fibre


Increased fibre in the diet may help to reduce calcium levels by binding with the calcium and reducing the amount of calcium that can be absorbed into the body through the gastrointestinal tract.

 

ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 states that "In dogs and cats with hypercalcemia, correcting or controlling hypercalcemia aids in preventing calcium oxalate urolith recurrence. Doing so is difficult in cats with idiopathic hypercalcemia and no single treatment has been shown to be effective, including glucocorticoids, bisphosphonate administration, or dietary modification using a high-fiber diet with potassium citrate administration, but 5 cats with idiopathic hypercalcemia had normalization of blood calcium concentrations when treated with a high-fiber diet.:

 

However, you do need to be careful when choosing a fibre. One type of fibre called fructooligosaccharides (FOS) may actually cause elevated calcium levels. See Nutritional Requirements for more information on fibre.

 

One food to discuss with your vet is Hill's w/d, which has added fibre. The canned version of this food would be suitable for most CKD cats, with a phosphorus level of 0.76% and a protein level of 37.80%. The phosphorus level in the dry food is a little higher at 0.80%, with a protein level of 40.56%, but this might still be acceptable if your cat's phosphorus levels are under control.

 

High Calcium Levels: Advanced Treatments


These treatments may be necessary if the simple treatments described above  do not resolve the problem. They all have pros and cons, and some of the cons are potentially serious. Discuss with your vet.

High Calcium Levels: Corticosteroids


Corticosteroids such as prednisolone may sometimes be used to control high calcium levels. Hypercalcemia in dogs and cats (2016) Peterson ME Merck Veterinary Manual says "Administration of prednisone results in longterm decreases in ionized and total calcium concentrations in some cats."

 

Using steroids can have certain undesirable side effects, see steroids for more information.

 

High Calcium Levels: Loop Diuretics Such As Furosemide (Lasix))


Furosemide (Lasix) is a loop diuretic. Diuretics are commonly used in heart disease, but may occasionally be used to help reduce high calcium levels, which they do by increasing the excretion of calcium via the kidneys.

 

Diuretics are not usually appropriate for CKD cats because they may increase the risk of dehydration, but be guided by your vet.

 

High Calcium Levels: Bisphosphonate Drugs: Alendronate (Fosamax)


If (and only if) ionised calcium levels are at least 25% above the normal upper limit, you could ask your vet about using bisphosphonate drugs. These medications are commonly used to treat humans with osteoporosis, and are occasionally used in hypercalcaemic cats. They help by encouraging the bones to absorb calcium, which then reduces calcium levels in the blood.

 

Alendronate (Fosamax)


One drug in this family is called alendronate (Fosamax). Treatment of ionized hypercalcemia in 12 cats (2006-2008) using PO-administered alendronate (2015) Hardy BT, de Brito Galvao JF, Green TA, Braudaway SR, DiBartola SP, Lord L & Chew DJ Journal of Veterinary Internal Medicine 29(1) pp200-6 looked at the use of alendronate in cats with idiopathic hypercalcaemia. The cats were given a dose of 5-20 mg orally every seven days. The study reduced calcium levels in all the cats with no major side effects and concludes "Alendronate was well tolerated and decreased iCa in most cats for the 6-month period of observation."

 

The usual starting dose is 10mg for cats, given orally only once a week, and many people opt for a twelve hour fast beforehand. The cat must stay upright for at least 15 minutes after taking it so as to avoid oesophageal damage. Always follow the treatment with a water chaser. Plumb's suggests buttering the cat's lips to encourage swallowing.  Alendronate dosing protocol for cats with idiopathic hypercalcaemia (2014) Peterson ME Insights into Veterinary Endocrinology discusses dosing.

 

Ionised calcium levels should be checked regularly, starting four weeks after the first dose, and the dose should be adjusted if necessary .

 

If you are using ranitidine (Zantac 75) intravenously for excess stomach acid (highly unlikely outside a hospital setting), be aware that it doubled the effect of alendronate in one human study.

 

There is some concern about using bisphosphonates in CKD patients. Plumb's Veterinary Drug Handbook states that "because of a lack of experience, the drug is not recommended for use in human patients with severe renal dysfunction." 

 

Drugs lists possible side effects of alendronate in humans.

 

Pamidronate


Another bisphosphonate is pamidronate. Uses and effectiveness of pamidronate disodium for treatment of dogs and cats with hypercalcemia (2005) Hostutler RA, Chew DJ, Jaeger JQ, Klein S, Henderson D, DiBartola SP Journal of Veterinary Internal Medicine 19(1) pp29-33 found it appeared to be safe and effective.

 

Use of bisphosphonates to treat severe idiopathic hypercalcaemia in a young Ragdoll cat (2011) Whitney JL, Barrs VR, Wilkinson MR, Briscoe KA & Beatty JA Journal of Feline Medicine & Surgery 13(2) pp129-34 discusses the case of a young cat with idiopathic hypercalcaemia who became clinically normal following the use of bisphosphonate drugs. Idiopathic means no obvious cause could be found.

 

However, pamidronate has to be given intravenously and may cause electrolyte imbalances. Like alendronate, it may be contraindicated for CKD cats.

 

High Calcium Levels: Calcitriol


Calcitriol is a hormone produced by the kidneys which helps to regulate parathyroid hormone (PTH). Some people use calcitriol as a supplement to try to control secondary hyperparathyroidism.

 

Although calcitriol may cause calcium levels to rise, in some cases it may actually be used to try to reduce calcium levels. However, this should only be attempted if ionised calcium is above midrange (or even at the top of the normal range), and an intermittent dosing schedule should be used. The causes and consequences of feline hypercalcemia (2009) Cook AK Presentation to the ACVIM Forum explains more about treatments for hypercalcaemia and mentions the use of calcitriol in CKD cats who have both elevated calcium and elevated ionised calcium levels. It states that if ionised calcium levels increase while using calcitriol for this purpose, it must be discontinued immediately.

 

See below for more information on calcitriol.

 

High Calcium Levels: Cancer


Although it is fairly rare, high calcium levels may be caused by cancer, so if the cause of your cat's hypercalcaemia is unknown, especially if you find the treatments above ineffective, it is worth asking your vet to test for cancer. The causes and consequences of feline hypercalcemia (2009) Cook AK Presentation to the ACVIM Forum explains more about this.

 

Treating paraneoplastic hypercalcemia in dogs and cats (2007) Fan TM, de Lorimier L-P, Lucas P & Lacoste H Veterinary Medicine May 2007 discusses possible treatment options in this situation (many of which are the same as those discussed above).

 


Elevated PTH and Secondary Hyperparathyroidism


 

Untreated elevated parathyroid hormone (PTH) levels may eventually lead to a condition called secondary hyperparathyroidism.

 

These are the treatments which may be used:

Secondary Hyperparathyroidism: Phosphorus Control


The first line of attack to reduce the risks of secondary hyperparathyroidism is to feed your CKD cat a diet low in phosphorus. If this is not sufficient, you should also use phosphorus binders.

 

For many cats, phosphorus control will be enough to avoid secondary hyperparathyroidism. Survival of cats with naturally occurring chronic renal failure: effect of dietary management (2000) Elliott J, Rawlings JM, Markwell PJ, Barber PJ Journal of Small Animal Practice 41(6) pp235-242 found that a low phosphorus diet, with added binders where necessary, prevented the rise in parathyroid hormone levels seen in the control cats whose phosphorus levels were not restricted. In fact, the cats who ate reduced phosphorus food or food with added phosphorus binders lived more than twice as long as those who did not.

 

Phosphorus control is such an important topic for CKD cats that there is a page devoted to the subject here, and a page devoted to phosphorus binders (which are used when dietary restriction of phosphorus is not sufficient to control phosphorus levels) here.

 

Secondary Hyperparathyroidism: Famotidine


Famotidine (Pepcid AC) is commonly used in CKD cats to block the production of excess stomach acid.

 

As a side effect it may reduce PTH levels in CKD patients. Famotidine reduces serum parathyroid hormone levels in uremic patients (1991) Arik N, Arinsoy T, Sayín M, Taşdemir I, Yasavul U, Turgan C, Caglar S Nephron 59(2) p333 explains more about this.

 

I would not use famotidine to treat elevated PTH levels only, but if you are using it anyway to control excess stomach acid, you may possibly see a reduction in PTH levels as well.

 


Secondary Hyperparathyroidism: Calcitriol


Calcitriol: What is It?


Calcitriol is the active form of Vitamin D. Despite its name, it is not the same as the vitamin D we eat or obtain from sunlight or supplements. Calcitriol is actually a hormone, and it plays an important part in regulating phosphorus and calcium levels in the body.

 

Here is how calcitriol is produced in the body:

  • Vitamin D2 (ergocalciferol) is found in some plant-based foods. 

  • Vitamin D3 (cholecalciferol) is produced in the skin when the skin is exposed to sunlight (which is a poor mechanism in cats, probably because of their fur coats), but may also be found in certain foods such as eggs.

  • Supplements containing vitamin D2 and vitamin D3 are also widely available (but not normally required in cats).

  • Vitamin D (whether D2 or D3) is converted in the liver into calcidiol (25-hydroxyvitamin D [25(OH)D], or 25-hydroxycholecalciferol).

  • Calcidiol is then converted in the kidneys into the biologically active form known as calcitriol (1,25-dihydroxyvitamin D [1,25(OH)2D], or 1,25 dihydroxycholecalciferol.

Levels of calcitriol tend to fall in CKD because the damaged kidneys are less efficient at concerting calcidiol into calcitriol. This is thought to be a factor in the development of secondary hyperparathyroidism.

 

Therefore human patients with secondary hyperparathyroidism are sometimes given additional calcitriol, and some people do the same for their CKD cats. The role of phosphorus in feline chronic renal disease (2010) Chew D & Kidder A CVC in San Diego Proceedings states "In some instances, PTH cannot be controlled despite dietary intervention and use of intestinal phosphate binders. Other treatments with calcitriol and calcimimetics may be indicated in these cases."

 

Mar Vista Vet has more information on calcitriol.

 

Calcitriol Debate


The use of calcitriol in cats is somewhat controversial, in part because no studies clearly show that it is effective for cats (although it does appear to be effective for dogs).

 

The willingness or otherwise of US vets to use calcitriol may depend in part upon which vet school they attended. Initial studies at Cornell University College of Veterinary Medicine and later studies at the University of Georgia College of Veterinary Medicine found that using calcitriol caused calcium levels to rise. However, Ohio State University College of Veterinary Medicine has also conducted research into the use of calcitriol in CKD cats, and it believes that the risk of hypercalcaemia is dosage dependent and that the risk can be managed.

 

Calcitriol: Pro


Calcitriol advocates believe that it is possible to have normal phosphorus levels and still have secondary hyperparathyroidism. They believe not only that the use of calcitriol is therefore essential, but also that calcitriol may help control uraemia and even slow the progression of CKD.

 

Benefits of calcitriol therapy and serum phosphorus control in cats and dogs with chronic renal failure. Both are essential to prevent or suppress toxic hyperparathyroidism (1996) Nagode LA, Chew DJ, Podell M Veterinary Clinics of North American Small Animal Practice 26 pp1293-1330 discusses the important of controlling secondary hyperparathyroidism in cats and the role of calcitriol in doing so.

 

Comparison of the effects of daily and intermittent-dose calcitriol on serum parathyroid hormone and ionized calcium concentrations in normal cats and cats with chronic kidney failure (2006) Hostutler RA, DiBartola SP, Chew DJ, Nagode LA, Schenck PA, Rajala-Schultz PJ, Drost WT Journal of Veterinary Internal Medicine 20(6) pp1307-13 was an early study into the use of calcitriol in cats. Unfortunately it found "At the dosages used, calcitriol treatment did not result in significant differences in serum parathyroid hormone concentrations before and after treatment in both normal cats and cats with chronic renal failure. With these dosages, adverse affects of calcitriol administration were not seen. Potential reasons for lack of apparent effect include small sample size, insufficient duration of study, insufficient dosage of calcitriol, problems with formulation or administration of calcitriol, and variable gastrointestinal absorption of calcitriol.”

 

Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease (2013) de Brito Galvao JF, Nagode LA, Schenck PA & Chew DJ Journal of Veterinary Emergency and Critical Care 23(2) pp 134–162 is a more recent paper which discusses calcitriol and its effectiveness  and renoprotective qualities for dogs and humans, but which concludes "Long-enough trials to determine any benefits for CKD cats treated with calcitriol have yet to be conducted."

 

Calcitriol: Con


There is evidence that you can control PTH levels and prevent, reverse or at least postpone the development of secondary hyperparathyroidism simply by controlling phosphorus levels. Feline hyperparathyroidism: pathophysiology, diagnosis and treatment of primary and secondary disease (2015) Parker VJ, Gilor C & Chew DJ Journal of Feline Medicine and Surgery 17(5) pp427-439 says “Treatment of RSHP includes controlling serum phosphorus concentrations by feeding a reduced phosphorus diet ± administration of a dietary phosphorus binder.”  See above for information on how to do this.

 

Chronic kidney disease (CKD) in dogs and cats - staging and management strategies (2015) Chew D Presentation to the Virginia Veterinary Medical Association 2015 Virginia Veterinary Conference says "Early phosphorus restriction in CRF has been shown in dogs and cats to blunt or reverse renal secondary hyperparathyroidism. In a study of cats with naturally-occurring CRF, renal secondary hyperparathyroidism was successfully managed by dietary restriction of phosphorus; one-third of the cats also required treatment with phosphorus binders.”

 

There is also some concern about the potential for calcitriol supplementation to cause both elevated phosphorus levels and elevated calcium levels. Renal Disease (2006) Polzin DJ Delaware Valley Academy of Veterinary Medicine states "the decision to use calcitriol must be made with caution because hypercalcemia is a potentially serious complication. Sustained calcitriol-induced hypercalcemia will likely result in reversible or irreversible reduction in GFR." GFR is a measure of kidney function.

 

Renal Disease (2006) Polzin DJ Delaware Valley Academy of Veterinary Medicine (2006) states "Nagode and colleagues have suggested that normalization of PTH levels using calcitriol therapy may provide clinical benefits that cannot be achieved by phosphorus restriction alone including amelioration of many clinical signs associated with CKD. We have been unable to completely substantiate these claims, but did find that calcitriol therapy significantly prolonged survival in dogs with stages 3 and 4 CKD."  He further states "A recommendation for or against routine use of calcitriol awaits results of properly designed controlled clinical trials."

 

What do I think? I tend to perch rather uncomfortably on the fence. Controlling secondary hyperparathyroidism is certainly important. Calcitriol may help with secondary hyperparathyroidism, and it does seem to help some cats feel better generally. I do not think using it is a bad idea if you follow the dosage and monitoring guidelines (see below) and stop it promptly if high calcium levels do result.

 

On the other hand, its advocates recommend starting it really early in order to prevent secondary hyperparathyroidism and I am not aware of any evidence for this being effective. Treatment recommendation for CKD in cats (2015) International Renal Interest Society states that calcitriol might be helpful for dogs in IRIS Stage 3 but that "beneficial effects of ultra low dose calcitriol have not yet been established in cats."

 

Overall, I would be happy to consider using calcitriol, but I do not consider it essential. If you can find it, and can afford it and the accompanying testing schedule, and your cat seems to tolerate it, then you could give it a go. If for whatever reason you are unable to use it, I would not be concerned.

 

Calcitriol: Considerations Before Starting


Calcitriol will not work for cats whose phosphorus levels are already above 8 mg/dl or 2.6 mmol/L, and is of limited value for cats with phosphorus levels above 6 mg/dl or 1.9 mmol/L. Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease (2013) de Brito Galvao JF, Nagode LA, Schenck PA & Chew DJ Journal of Veterinary Emergency and Critical Care 23(2) pp 134–162 says “Serum phosphorus should be less than 1.9 mmol/L [<6.0 mg/dL] before starting calcitriol treatment and thereafter to ensure calcitriol efficacy in PTH suppression."

 

Therefore, if your cat's phosphorus levels are above 6 mg/dl or 1.9 mmol/L, you must take all possible steps to control phosphorus levels (see Phosphorus for information on how to do this) before using calcitriol.

 

Calcitriol may cause ionised calcium levels to increase. Prolonging life and kidney function (2007) Chew D Presentation to the 32nd World Small Animal Veterinary Association World Congress explains more about this.

 

On the other hand, Chronic kidney disease (CKD) in dogs and cats - staging and management strategies (2015) Chew D Presentation to the Virginia Veterinary Medical Association 2015 Virginia Veterinary Conference mentions that calcitriol will be less effective if your cat's ionised calcium level is low.

 

You also need to consider your cat's total calcium levels. If your cat's calcium level x phosphorus level is over 60-70 in US values or over 5 in international values, your cat is at risk of soft tissue mineralisation (see Diagnosis), and since calcitriol may raise calcium levels, you should not use it until this level has been reduced. Chronic kidney disease (CKD) in dogs and cats - staging and management strategies (2015) Chew D Presentation to the Virginia Veterinary Medical Association 2015 Virginia Veterinary Conference states: "Calcitriol should not be administered until hyperphosphatemia has been controlled. If the Ca X P solubility product exceeds 60-70, calcitriol should be avoided because of the risk of soft-tissue mineralization." This also applies if you multiply phosphorus by ionised calcium, and the level is higher than 8.75 in US values or 35 in international values.

 

Calcitriol: When to Start


As stated earlier, calcitriol is not an essential treatment, so if you are unable to obtain it or cannot afford it, or if it does not seem to agree with your cat, I would give it a miss.

 

Please also see Calcitriol: considerations before starting.

 

If you and your vet do decide to use calcitriol, and wish to start before your cat's PTH levels are elevated, Dr Larry Nagode, formerly of Ohio State University College of Veterinary Medicine, now sadly deceased, advises starting calcitriol when creatinine reaches 2 mg/dl or 175 mmol/L, assuming pre- and post-renal causes of the elevated creatinine have been ruled out.

 

Calcitriol: Dosage


Calcitriol: Dosage Amount


The usual dose recommended for cats by Ohio State University College of Veterinary Medicine is 2.5-3.5 ng per kg of bodyweight orally each day. Note this is nanograms, not milligrams. These are tiny amounts, so in practice you must use compounded calcitriol in order to obtain cat-sized doses (see below for sources).

 

Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease (2013) de Brito Galvao JF, Nagode LA, Schenck PA & Chew DJ Journal of Veterinary Emergency and Critical Care 23(2) pp 134–162 says "Doses lower than 2.5 ng/kg are rarely used, and occasionally a dose as high as 6ng/kg/day is used when lower doses do not succeed in lowering PTH."

 

Initially the dose will probably be based to a degree on your cat's creatinine levels, So, for example, if your cat's creatinine level is 2 mg/dl, you might start at 2.5 ng/kg, but if your cat's creatinine level is 4 mg/dl, your vet might suggest starting at 3.5 ng/kg. Once you know your cat's PTH levels (you should be monitoring PTH levels once you have begun calcitriol), your vet will probably use that as a guide when deciding whether to adjust the dose.

 

Calcitriol: Dosage Frequency


Calcitriol used to be given daily, which requires tiny amounts. Therefore there has been research into giving it in slightly larger amounts but less frequently, sometimes referred to as intermittent dosing.

 

Comparison of the effects of daily and intermittent-dose calcitriol on serum parathyroid hormone and ionized calcium concentrations in normal cats and cats with chronic kidney failure (2006) Hostutler RA, DiBartola SP, Chew DJ, Nagode LA, Schenck PA, Rajala-Schultz PJ, Drost WT Journal of Veterinary Internal Medicine 20(6) pp1307-13 found that intermittent dosing did not seem to make any difference in terms of effectiveness. It can also work out cheaper, and may reduce the risk of hypercalcaemia. It is recommended that intermittent dosing be used for cats whose calcium levels are at the high end of the normal range.

 

Therefore most people these days use an intermittent dosing schedule, giving calcitriol every 3.5 days, in which case the standard dose is 8.75 - 12.25 ng twice a week.

 

The timing must be exact, i.e. every 3.5 days rather than every three days or every four days, so many people use a schedule of giving it on Wednesday evenings and Sunday mornings, at a time to suit (e.g. 10 a.m. Sunday and 10 p.m. Wednesday).

 

For a 10lb (4.5kg) cat, this works as follows:

  •  If you are giving the 2.5 ng starting dosage of calcitriol to this cat, you would be giving a total of 11.4 ng a day.

  • If you are giving it every 3.5 days, you would give 38.8 ng (11.4ng per day x 3.5 days).

  • This would be rounded up to 39 ng.

To work this out for your own cat, do as follows:

  • Take your cat's body weight in pounds and divide by 2.2 to get the equivalent in kg.

  • Take your cat's body weight in kg and multiply by your daily dose, e.g. 2.5 ng.

  • Multiply the result by 3.5 (days).

For example, let's say your cat weighs 7 lbs:

  • 7.5lb divided by 2.2 = 3.41kg

  • 3.41 kg x 2.5ng/kg per day = 8.53ng

  • 8.53ng x 3.5 days = 29.86ng

  • Round it, so your cat's dose would be 30ng twice a week (every 3.5 days).

In practice your vet should tell you how much to give.

 

Calcitriol: Pulse Dosing


Occasionally pulse dosing may be considered for cats whose PTH levels do not reduce as expected on calcitriol. In such cases, you give a dose of 20ng/kg twice weekly for three weeks, followed by 10ng/kg twice weekly dosing for 2-3 weeks, after which you test PTH levels. If the PTH level is still more than three times the top of the normal range, you repeat the pulse dosing. One or two sessions of pulse dosing are normally sufficient to get PTH levels down, after which normal dosing may continue as outlined above.

 

Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease (2013) de Brito Galvao JF, Nagode LA, Schenck PA & Chew DJ Journal of Veterinary Emergency and Critical Care 23(2) pp 134–162 explains more about pulse dosing.

 

Calcitriol: How to Give


The amounts needed are tiny, so the treatment has to be compounded into the correct dosage for a cat (see below for suppliers).

 

Calcitriol is provided in either oil-filled capsules or oily liquid form. If you are using a liquid formulation, be sure to give it into the side of the mouth, not into the front.

 

Cats receiving calcitriol daily do not need to be fasted beforehand unless their blood calcium levels are near the top of the range, in which case they should be fasted for 2-4 hours before giving the calcitriol and for 30-60 minutes afterwards.

 

Cats receiving calcitriol every 3.5 days should ideally be fasted for 2-4 hours before giving the calcitriol and for an hour afterwards. If their blood calcium levels are near the top of the range, the fasting is very important.

 

You should avoid giving any supplements etc. containing calcium on the days when you give calcitriol.

 

Do not store liquid calcitriol in the fridge. Do not shake it.

 

Calcitriol: Monitoring


With standard dosing, it is usual to start with the lowest dose. Many people check PTH, calcium and phosphorus levels after 10-14 days, though Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease (2013) de Brito Galvao JF, Nagode LA, Schenck PA & Chew DJ Journal of Veterinary Emergency and Critical Care 23(2) pp 134–162 says "After receiving the initial dose for 2 months, a recheck of serum PTH concentration will indicate if an incremental calcitriol dosage increase is necessary."

 

If you are using pulse dosing, you would normally check 5-6 weeks after starting pulse dosing.

 

Your goal is to reduce PTH levels, whilst keeping phosphorus levels low and calcium levels within normal range. If the levels are acceptable, you should check again after about a month. If they still are out of range, adjust the dose and check again after 10-14 days. Once you have determined the correct dose, you should continue to check PTH, calcium and phosphorus levels every 4-8 weeks.

 

You should wait at least 24 hours after giving a dose of calcitriol before running these blood tests.

 

It is not normally necessary to fast your cat before testing, but I would not check immediately after eating - aim to keep food away from your cat for about four hours before the blood is taken. Dr Nagode has stated that waiting 1-2 hours is probably acceptable.

 

Calcitriol Side Effects and interactions


MedlinePlus lists possible side effects, including weakness, vomiting, constipation, and increased urination, especially at night.

 

Some cats seem to feel a little off colour on the days when they are given calcitriol. In such cases, the twice weekly dosing schedule seems to work better.

 

Using calcitriol may increase your cat's phosphorus levels. Keep an eye on this, and increase your phosphorus binder dose as necessary. Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease (2013) de Brito Galvao JF, Nagode LA, Schenck PA & Chew DJ Journal of Veterinary Emergency and Critical Care 23(2) pp 134–162 says "If hyperphosphatemia develops during calcitriol treatment, due to further loss of renal excretory function or less likely more intestinal absorption, it is necessary to increase the extent of dietary phosphate restriction and/or to increase the dose or class of intestinal phosphate binder with use of a combination of binders (eg, aluminum, lanthanum, and sevelamer carbonate) thus minimizing any toxic effects of each individual class of binder.”

 

Calcitriol may also cause your cat's calcium levels to rise too far. If this happens, you will probably have to stop using calcitriol, after which calcium levels should reduce within a few days or so.

 

According to Plumb's Veterinary Drug Handbook, corticosteroids may cancel out the effects of calcitriol. This is because calcitriol increases calcium absorption, whereas corticosteroids inhibit calcium absorption.

 

Calcitriol Sources


Since cats need only tiny doses of calcitriol, you usually have to have it compounded. Calcitriol comes in an oily suspension, and the compounding pharmacy normally needs to dilute this further with more oil in order to create cat-sized doses. The end product is supplied in either a liquid, oily form, or is hardened and supplied in capsules.

 

Most compounding pharmacies should be able to do this in theory, but you need a pharmacist who is used to producing these strengths and able to ensure that the medication is evenly distributed throughout the end product. Below are details of pharmacies that people have used with success.

 

USA


If you buy six months supply at a time, it works out at about US$10-40 a month. If you do buy six months' supply at a time, make sure its shelf life is for six months or longer.

 

These compounded pharmacies are often recommended in the USA:

 

Thriving Pets


Thriving Pets

 

Offers calcitriol (via Regional Pharmacy's licence) in pre-set concentrations:

  •     40 ng/ml

  •     80 ng/ml

  •   100 ng/ml

  •   160 ng/ml

  •   240 ng/ml

  •   320 ng/ml

  • 1000 ng/ml

Therefore your vet will need to decide which concentration to use in order to get the dosage which you need. Thriving Pets can help you with this if necessary, just call them.

 

f you enter the word "tanya" (without the ") in the promotional code box, you will receive a 10% discount on orders over US$100.

 

Ballard


Ballard Plaza Pharmacy

In Seattle is used by some people, though I understand they do not ship to California. From what I hear, their prices are quite reasonable.

 

Triad


Triad Compounding

Sell calcitriol in various strength including 196ng/ml. I have heard that they may be relatively expensive, but do not know their current pricing levels.

 

Wells


Wells Pharmacy Network

Took over the business of Francks Pharmacy, which closed in July 2012 following problems with quality control. Available strengths include 256ng/ml and 320ng/ml. Some people use Wells and are happy but I have heard that Wells are now only prepared to ship 7ml at a time (with a shelf life of 120 days) and that the price has increased in recent years. 

 

US Compounding


US Compounding

Some people have used US Compounding for many years, but I have very little information about them.

 

UK


The use of calcitriol is difficult in the UK, because it is very hard to find a pharmacy which is authorised to compound medications for veterinary use into cat-sized dosages. Some people use human calcitriol but I'm not too clear how they manage to obtain cat-sized doses from it.

 

If you can find a vet with a US licence who can write a prescription for calcitriol, Thriving Pets will fill it for you.

 

If you are unable to obtain calcitriol, please do not be too despondent. It is not an essential treatment for most CKD cats. If you focus on phosphorus control, for many cats this will be sufficient to avoid secondary hyperparathyroidism, except possibly for very end stage cats. 

 

Calcitriol Groups


You can discuss the use of calcitriol on Tanya's CKD Support Group, though not too many members use it. There are also groups dedicated to its use, though as you might  expect, these groups focus on the positive aspects of the treatment.

 

Calcitriol Pets is a small support group for people using calcitriol in their cats.

 

Calcitriol Group is a group devoted to discussing the use of calcitriol in cats and dogs.

 


Calcimimetics


 

Calcimimetics are a family of drugs which are used in humans to treat secondary hyperparathyroidism and hypercalcaemia caused by parathyroid cancer. Occasionally these medications are used to treat severe secondary hyperparathyroidism in CKD cats.

Cinacalcet (Sensipar)


Cinacalcet (Sensipar) was approved by the US Food and Drug Administration in March 2004 for the treatment of secondary hyperparathyroidism in humans. Cinacalcet hydrochloride (Sensipar) (2005) Poon G Baylor University Medical Center Proceedings 18(2) pp182-184 gives an overview of cinacalcet.

 

Health Canada reports that in 2007 the use of cinacalcet in humans was restricted to those on dialysis because it was found that patients receiving cinacalcet who were not on dialysis were more likely to develop low calcium levels.

 

Cinacalcet is occasionally used in CKD cats for whom other attempts to reduce parathyroid hormone levels have not worked. The role of phosphorus in feline chronic renal disease (2010) Chew D & Kidder A CVC in San Diego Proceedings states "In some instances, PTH cannot be controlled despite dietary intervention and use of intestinal phosphate binders. Other treatments with calcitriol and calcimimetics may be indicated in these cases."

 

Cinacalcet works by lowering calcium levels, so should not be used in patients with low calcium levels. It is very expensive. I have only heard of a couple of people who have used it in cats, and never heard back to see how they got on with it.

 

Elevated PTH levels can contribute to anaemia. Improved parathyroid hormone control by cinacalcet is associated with reduction on darbepoetin requirement in patients with end-stage renal disease (2011) Battistella M, Richardson RM, Bargman JM & Chan CT Clinical Nephrology 76(2) pp99-103 found that cinacalcet meant less treatment for anaemia was required in human patients. I don't think this is unique to cinacalcet, but rather because of the reduction in PTH levels.

 

Amgen - prescribing information from the manufacturer.

 

MedlinePlus explains more about cinacalcet.

 

Etelcalcetide


Etelcalcetide is another member of the calcimimetic family which is marketed under the name Parsabiv. It was approved in the USA in 2017 for the treatment of secondary hyperparathyroidism in humans on dialysis. I am not aware of any usage in cats to date.

 

Amgen - prescribing information from the manufacturer.

 

 

 

 

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This page last updated: 11 April 2018

Links on this page last checked: 11 April 2018

 
   

*****

 

TREATING YOUR CAT WITHOUT VETERINARY ADVICE CAN BE EXTREMELY DANGEROUS.

 

I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who has lived through CKD with three cats. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.

 

If your cat appears to be in pain or distress, do not waste time on the internet, contact your vet immediately.

 

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