Tanya's Comprehensive Guide to Feline Chronic Kidney Disease

If your cat's phosphorus level (in blood tests) is over 6 US or 1.9 international, it is too high and you need to get it under control.
Doing this should help slow the progression of the CKD, reduce the risk of serious problems (including heart problems) and make your cat feel better.
Feeding a food low in phosphorus is the first step. Ideally you want a food with a level below 0.5% phosphorus on a dry matter analysis basis. Prescription kidney foods are really the only foods which meet this criterion.
If your cat will not eat the prescription diet, feeding a food as low in phosphorus as possible and adding a phosphorus binder to the food when appropriate can help control your cat's phosphorus levels.

Why Phosphorus is So Important for CKD Cats Back to Page Index

Phosphorus is a mineral essential for good health which is contained in many foods. The body is very good at regulating its phosphorus levels by removing excess phosphorus via the kidneys. However, the kidneys of a CKD cat can no longer efficiently excrete excess phosphorus, so the vast majority of CKD cats will eventually have levels of phosphorus in their blood which are too high: this is known as hyperphosphataemia.

In contrast to the protein debate, there is no dispute about the importance of treating hyperphosphataemia because:

High phosphorus levels can make CKD progress more quickly.

They can cause a variety of unpleasant symptoms; and

They can adversely affect calcium levels and eventually can trigger problems with a hormone called parathyroid hormone (PTH), causing a serious condition called secondary hyperparathyroidism (which is not the same thing as hyperthyroidism, although Cornell Universiy College of Veterinary Medicine does mention that around 20% of cats with hyperthyroidism also have elevated phosphorus levels).
In Chronic kidney disease in dogs and cats: the pivotal role of phosphorus control (2011) A Presentation to the 63rd CVMA Convention, Dr D Chew states that it is possible for a CKD cat to develop secondary hyperparathyroidism even if phosphorus levels and ionised calcium levels are normal. He explains "In the early stages of chronic kidney disease increased levels of parathyroid hormone (PTH) keep serum phosphorous within the normal range by increasing phosphate excretion into urine. This allows for normalization of serum phosphorous at the expense of hyperparathyroidism." Therefore, even a cat with normal phosphorus levels but with elevated PTH levels would benefit from phosphorus restriction.

high phosphorus levels may reduce the cat's response to ESAs, a treatment used for severe anaemia, which is relatively common in CKD cats.

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 the cats who ate reduced phosphorus food or food with added phosphorus binders lived more than twice as long as those who did not.

Thus, focusing on phosphorus control is one of the most effective ways to help your CKD cat feel better and live longer. The good news is, it's not usually too difficult or expensive to do either.

Symptoms of Hyperphosphataemia Back to Page Index

There are a number of different symptoms of high phosphorus levels. You may not see all of these symptoms, and some of them may have other causes as outlined under each symptom, but if you see any of the symptoms described below, please ensure that your cat's phosphorus level is checked and is no higher than 1.9 mmol/L/l in international measurements or 6 mg/dl in US measurements.

Loss of appetite

Lack of co-ordination in the limbs

Plantigrade posture

Itching

Weight loss

Weakness

Teeth grinding

"Knuckling"

Nausea

Twitching, trembling or shaking

Loss of Appetite

High phosphorus levels can make a cat feel bad and lead to a loss of appetite, particularly if secondary hyperparathyroidism develops.

Other causes include levels of toxins in the blood which may cause stomach acid, anaemia, crashing, metabolic acidosis, mouth ulcers, fluid build-up, the use of antibiotics, constipation or the use of medication for hyperthyroidism. Dental problems may also cause loss of appetite.

Cats who do not eat are at risk of developing a potentially life-threatening condition known as hepatic lipidosis; Mar Vista Vet has more information about this. Therefore, it is important to try to find the cause and treat it as quickly as possible.

Itching

Itching is fairly common in cats with high phosphorus levels, particularly if the high phosphorus levels go untreated, resulting in secondary hyperparathyroidism.

Itching may also be caused by general levels of toxins in the blood. Alternatively itching may indicate a Vitamin B deficiency or be a sign of an essential fatty acids deficiency. Itching on the face in particular may be a side effect of the medication for hyperthyroidism. Occasionally itching can be a sign of liver problems; if this is the case, your cat's bloodwork should show elevated liver values.

Lack of Co-ordination in the Limbs/Back Leg Weakness

This can be due to high phosphorus levels interfering with the nerve messages that control the limbs, a condition known as neuropathy. Some of the symptoms include "forgetting" where the hind legs are (getting up and leaving without them, for instance, or leaving them in the air even after licking them), or stumbling and feet crossing over when walking.

Knuckling

"Knuckling" may also be seen, where the cat walks on the top of the foot with the toes tucked underneath, appearing almost to be dragging the toes behind. I haven't been able to find a photo of a cat with high phosphorus levels doing this, but the University of Florida Veterinary Medical Teaching Hospital has a photo of a dog with a similar problem.

Plantigrade Posture

You may also see a plantigrade posture (as demonstrated by Ollie to the left), where the cat walks on his/her hocks instead of his/her feet: this is most common in diabetic cats, but may sometimes be seen in cats with high phosphorus levels, or with neurological problems from other causes. Ollie did this because of low potassium levels. Since Ollie is so fluffy, you may find this photo on 123catworld clearer. Long Beach Animal Hospital has a photograph of a cat with diabetic neuropathy doing this (click on Symptoms). Newman Veterinary has a good before and after photo of a diabetic cat with this problem, scroll down a little to Other Common Consequences, then click on Plantigrade Stance (in red font).

University of Chicago Jack Miller Center for Peripheral Neuropathy is a human site which discusses uraemic neuropathy (neuropathy caused by CKD).

Teeth Grinding

This may be a sign of "rubber jaw", caused by a condition related to the CKD called secondary hyperparathyroidism.

Other more common causes of teeth grinding include excess stomach acid, dental problems and dehydration.

Animal Dental Center of Milwaukee and Oshkosh discusses the various courses of teeth grinding in cats.

Youtube has a video of a cat grinding his/her teeth (if you're a member of youtube, which I am not, please post to point out that this is no laughing matter but indicates a need for veterinary attention to find out the cause in this poor cat's case).

Weakness

Weakness and muscle wasting may be seen, especially in the back legs. This can be caused by high phosphorus levels leading to secondary hyperparathyroidism.

Weakness in the back legs is often caused by low potassium levels or occasionally by low magnesium or low calcium levels; while muscle wasting may be caused by metabolic acidosis. General weakness may be caused by anaemia. If your cat no longer jumps, this may be thought to be weakness when in fact it is an unwillingness to jump because of blindness caused by hypertension. An inability to jump or climb may also be caused by arthritis.

If your cat suddenly cannot walk properly on one leg, particularly a back leg, and the leg feels cold to the touch, this may indicate a heart-related problem known as a saddle thrombus. This is a medical emergency, and you need to contact your vet as soon as possible.

Weight Loss

This may be caused by high phosphorus levels.

Other causes include proteinuria and electrolyte imbalances. Cats with metabolic acidosis often lose muscle tone as well as weight - in particular, they may have a bony spine. Weight-loss may also be a symptom of other diseases such as diabetes or hyperthyroidism. Other possible causes include IBD (Inflammatory Bowel Disease) or cancer.

Purina has a Body Condition diagram showing how to gauge your cat's physical condition.

Nausea

High phosphorus levels and the resulting secondary hyperparathyroidism may cause nausea, which may be manifested as a lack of appetite.

Alternatively, vomiting clear foam is a classic symptom for a CKD cat, and is usually caused by toxin levels, particularly excess stomach acid. Occasionally vomiting is caused by constipation, particularly if your cat vomits before, during or immediately after using the litter tray. Anaemia or metabolic acidosis may also cause nausea.

Twitching, Trembling or Shaking

Twitching may be caused by high phosphorus levels.

Other causes of twitching include high or low potassium levels, high blood pressure, calcium imbalances (especially head twitching), a hyperactive thyroid or Vitamin B deficiency. Twitching may also be caused by high toxin levels. If your cat only twitches while you are giving fluids, it is probably caused by either the type of fluid used or by giving cold (room temperature) fluids.

Pharaoh's Shakes is a video showing a CKD cat twitching.

Goal for Phosphorus Level in Bloodwork Back to Page Index

Your vet can determine if your cat's phosphorus levels are too high by checking your cat's bloodwork for phos, P or Pi (these are all abbreviations for phosphorus). Most vets do this routinely, but if yours doesn't, ask for it to be done.

Your cat may have phosphorus levels within normal limits, but many vets forget that the higher limits only apply to growing kittens. In Chronic kidney disease in dogs and cats: the pivotal role of phosphorus control (2011) A Presentation to the 63rd CVMA Convention, Dr D Chew states "Serum phosphate levels are maintained within a narrow range in health. Young growing animals often have higher levels of serum phosphorous than adults. The normal serum phosphorous range of many laboratories includes that of adults and growing animals which may make it difficult to detect early rises in serum phosphorous above normal. The typical normal range for phosphorus in the cat is 2.5-6 mg/dL (0.81 to 1.94 mmol/L)."

A few years ago the University of Texas Health Science Center gave the following ranges for healthy cats of differing ages:

Age	Phosphorus Range (US Values)	Phosphorus Range (International Values)
10 days - 2 years	4.5 - 6.7 mg/dL	1.45 - 2.16 mmol/L
2 years - 12 years	4.5 - 5.5 mg/dL	1.45 - 1.80 mmol/L
Over 12 years	2.7 - 4.5 m/dL	0.90 - 1.45 mmol/L

As the table shows, even a healthy older cat should have phosphorus levels in the bottom half of most laboratory ranges.

Vets may also forget that, if the cat's phosphorus multiplied by calcium is higher than 70 (US) or 5 (international), the cat is at risk of tissue calcification (see secondary hyperparathyroidism).

So if your vet tells you your cat's phosphorus level is fine, don't just take that at face value, ask for the exact level. Chances are it is too high for a CKD cat.

Ideally you want to get the level down to 4.0 (US) or 1.3 (international) but as the CKD progresses, this may become more challenging. The tables below give goals for phosphorus control based on the stage of CKD that your cat is in, based on guidelines from the International Renal Interest Society. Don't forget, these stages apply to stable cats; if your cat is dehydrated, for example, the bloodwork will not be accurate.

US Values

Stage of CKD	Creatinine Level	Phosphorus Target
IRIS Stage 2	Creatinine between 1.6 and 2.8 mg/dl	Below 4.5 mg/dl
IRIS Stage 3	Creatinine between 2.9 and 5.0 mg/dl	Below 5.0 mg/dl
IRIS Stage 4	Creatinine over 5.0 mg/dl	Below 6.0 mg/dl

International Values

Stage of CKD	Creatinine Level	Phosphorus Target
IRIS Stage 2	Creatinine between 140 and 249 mmol/L	Below 1.45 mmol/L
IRIS Stage 3	Creatinine between 250 and 439 mmol/L	Below 1.6 mmol/L
IRIS Stage 4	Creatinine over 440 mmol/L	Below 1.9 mmol/L

Summary of Phosphorus Goals

USA

take action as soon as your cat's phosphorus level goes above 6 mg/dl.

if your cat's level is between 4.5 and 6 mg/dl, but multiplying it by your cat's calcium level gives you a reading of 60-70 or over, take action now.

your aim is to reduce your cat's phosphorus to a level of 4 mg/dl. You may not be able to get it this low if your cat is in IRIS Stage 3 or 4, but aim never to let it go above 6 mg/dl.

if your cat's level is above 6 mg/dl, you can read below about ways to reduce the level. Check phosphorus levels every month to see if any adjustments to your treatment plan are necessary.

low phosphorus levels (below 4 mg/dl) are extremely rare in CKD cats, but are generally not considered to be a problem, although they may occasionally cause lethargy if present.

if your cat is very young (6-12 months old), then a higher level is appropriate, because kittens need phosphorus for their bones to grow properly. Check out the table above and discuss with your vet what would be an acceptable level.

Rest of the World

Take action as soon as phosphorus goes above 1.9 mmol/L/l.

If your cat's level is between 1.45 and 1.9 mmol/L/l, but multiplying it by your cat's calcium level gives you a reading of 5 or over, take action now.

Your aim is to reduce it to a level of 1.3 mmol/L/l. You may not be able to get it this low if your cat is in IRIS Stage 3 or 4, but aim never to let it go above 1.9 mmol/L/l.

If your cat's level is above 1.9 mmol/L/l, you can read below about ways to reduce the level. Check phosphorus levels every month to see if any adjustments to your treatment plan are necessary.

Low phosphorus levels (below 1.3 mmol/L/l) are not normally present in CKD cats, but are generally not considered to be a problem.

If your cat is very young (6-12 months old), then a higher level is appropriate, because kittens need phosphorus for their bones to grow properly. Check out the table above and discuss with your vet what would be an acceptable level.

If your vet refuses to accept that a phosphorus level above 6 mg/dl (US) or 1.9 mmol/L/l (international) is too high for your cat, print out and show him/her some of these references:

Dr Jonathan Elliott of the Royal Veterinary College states on page 14 that "the goal should be to keep the serum phosphorus concentration at the lower end of the reference range".

Phosphatemia management in the treatment of chronic renal disease: a round table discussion (2006) states "practitioners need to realise that a phosphate in the normal range could still be abnormal in renal patients". Page 6 provides detailed recommendations on phosphorus control.

Dr David Polzin of the College of Veterinary Medicine of St Paul's in Minnesota states that phosphorus binders should be begun "when serum phosphorus concentration exceeds 6.0 mg/dl."

Ways to Control High Phosphorus Levels Back to Page Index

Controlling phosphorus levels with diet

Controlling phosphorus levels with phosphorus binders

There are two main ways to control phosphorus levels, through dietary changes or by using phosphorus binders.

Controlling Phosphorus Levels with Diet

The most effective way to control phosphorus levels is by feeding foods low in phosphorus.

In Management of feline chronic renal failure (1998) Waltham Focus 8 (3) Dr Scott Brown states that ideally you want to feed a food with a phosphorus level under 0.5% on a dry matter analysis (DMA) basis (which is different to the percentage given on the can).

Most of the prescription renal diets have phosphorus levels below 0.5%, which is one of the main reasons why these foods were developed (there are other factors, see Which Foods to Feed).

If your cat won't eat the prescription foods, you still need your cat to eat. Many people seem to think that a food below 1% phosphorus on a dry matter analysis (DMA) basis is low phosphorus but that's not the case; you want to get as close to prescription food levels as possible.

In the USA, the minimum level of phosphorus in a non-prescription food is 0.5%, so you are not going to find a commercial food with phosphorus below this; but if you check the food data tables in the Diet and Nutrition section, you can try to find a food which your cat will eat with a level of phosphorus as close to 0.5% as possible.

Even if your cat's phosphorus level is normal, it is wise to feed a CKD cat a food as low in phosphorus as you can, because the less phosphorus your cat eats, the less work there is for the kidneys to do trying to process it; plus phosphorus levels tend to rise as the CKD progresses, and usually it is easier to keep them low rather than have to reduce them.

Controlling Phosphorus Levels with Phosphorus Binders

If your cat will not eat a prescription diet, or if his/her phosphorus levels are still too high despite feeding such a diet, products called phosphorus binders are used. These are simply added to the cat's food: they bind with some of the phosphorus in the food in the intestine, thus preventing it from being absorbed and therefore reducing levels of phosphorus in the cat's body.

Phosphorus binders are usually used when phosphorus levels are over 6 mg/dl (US) or 1.9 mmol/L/l (international). Once you start using binders, the goal is to get phosphorus down to a level of around 4 mg/dl (US) or 1.3 mmol/L/l (international).

To be effective, phosphorus binders should be given before or with food. You should start to see a difference in phosphorus levels around 7-10 days after starting binders. There are instructions on how to give binders below.

Using binders is not as effective as feeding a low phosphorus diet, because binders cannot bind all the phosphorus in the food, so your cat will still be absorbing some of the phosphorus. Therefore, even if you do have to feed a non-prescription diet (because the most important thing is that your cat eats), you should still aim to feed the lowest phosphorus food that your cat will eat. Many people seem to think that a food below 1% phosphorus on a dry matter analysis (DMA) basis is low phosphorus but that's not the case, particularly when you consider that most of the prescription renal diets have phosphorus levels below 0.5%. Aim for as low a phosphorus level as you can. The Diet and Nutrition section has links to food data tables for you to check out the phosphorus levels of various cat foods. I'm not recommending any of these foods, this is simply a list in order of phosphorus content.

You should not normally need to use binders if your cat is eating a prescription kidney diet, because this should be sufficient to control your cat's phosphorus levels. However, this is not always the case, particularly as the CKD worsens. If your cat's phosphorus levels are over 6 mg/dl (US) or 1.9 mmol/L/l (international) despite feeding a prescription diet, speak to your vet about adding binders.

If your cat isn't eating, there is little point giving phosphorus binders because your cat isn't ingesting any phosphorus in the food that needs binding. However, if you assist feed (as you should if your cat is not eating), you can add binders to the mixture.

All About Phosphorus Binders Back to Page Index

Phosphorus binders are used if feeding foods lower in phosphorus levels, such as prescription diets, does not keep your cat's blood phosphorus levels in the desired range (see above). They work by binding with some of the phosphorus in the cat's food in the intestine, thus preventing it from being absorbed and therefore reducing levels of phosphorus in the cat's body.

Over the counter antacids are commonly used for this purpose, and there are two main types: aluminium-based products and calcium-based products. Recently, branded products have also been released, including Ipakitin/Epakitin (which is calcium-based) and Renalzin (which contains a new type of binder called lanthanum carbonate).

The most popular binders are made from aluminium hydroxide. Overall these are the best choice because they are very effective, are available over the counter, are cheap, and have no taste or smell so most cats are prepared to eat them. Therefore these are what I recommend, but I do cover all binder types below.

Aluminium based binders

Calcium based binders (includes Ipakitine/Epakitin)

Other binders (includes Renalzin and Fosrenol)

Letting Other Family Cats Eat Food Containing Binders

It does not matter if your non-CKD cats eat some of your CKD cat's food containing phosphorus binders. However, please make sure that they also eat some food each day that does not contain binders. This is particularly important for kittens, who need twice as much phosphorus each day as a healthy cat because they are still growing.

Aluminium-Based Binders Back to Page Index

There are three types of aluminium-based binders, but aluminium hydroxide is generally considered to be the best choice.

Aluminium magnesium hydroxide

Sucralfate (sucrose aluminium hydroxide)
The best binder: aluminium hydroxide

Aluminium Magnesium Hydroxide

These binders, as the name suggests, also contain magnesium. Brand names include Maalox, Mylanta, Milk of Magnesia or Aludrox. Binders containing magnesium are not suitable for CKD cats because they can cause high magnesium levels in the blood, which in turn can sometimes cause urinary tract problems such as stones in some cats.

Pet Education states "Do not use magnesium containing products in animals with kidney failure."

Sucrose Aluminium Hydroxide

Sucrose aluminium hydroxide is also known as sucralfate or Carafate. It coats the digestive tract, so is commonly used to treat mouth ulcers or gastro-intestinal bleeding. Some British vets also recommend sucralfate as a phosphorus binder. One old study, Changes in serum phosphorus, calcium and alkaline phosphatase due to sucralfate (1986) Vucelić B, Hadzić N, Gragas J, Puretić Z International Journal of Clinical Pharmacology, Therapy and Toxicology 24(2) pp93-6, did find sucralfate was effective as a binder in humans, but it is not usually recommended as a phosphorus binder in cats. If you are unable to obtain aluminium hydroxide, however, it could certainly be worth considering, though I don't know the correct dosage for using it as a phosphorus binder.

If you are using sucralfate for mouth ulcers or gastro-intestinal bleeding at the same time as using aluminium hydroxide as a phosphorus binder, you might be able to reduce your dosage of aluminium hydroxide.

Aluminium Hydroxide: The Best Binder Back to Page Index

Dosage
Tips on how to give

Cautions and interactions

This is the most effective binder and the one I recommend because it is available over the counter (though you may have to use mail order in the USA), cheap, and if you buy the correct type it is odourless and tasteless. Unfortunately many vets are reluctant to prescribe aluminium-based binders because they think cats hate the taste. If they do prescribe them, they then often prescribe AlternaGel, a peppermint-flavoured binder which most cats hate, so it then becomes a self-fulfilling prophecy. AlternaGel also contains potassium citrate, which is not a good idea because citrate can increase the absorption of aluminium within the body.

I recommend instead that you look into buying aluminium hydroxide binders which are tasteless and odourless, and which most cats do not seem to notice in their food. See below for information on the various brands and links to mail order suppliers who can ship to UK, USA, Canada and Australia. Contrary to what some vets and pharmacists seem to believe, you do not need a prescription to buy these products.

Aluminium Hydroxide Binders Dosage

Naturally you must seek your vet's advice on the most suitable dosage for your cat; but generally speaking, the appropriate dosage for aluminium hydroxide based binders is as follows:

USA

Current Phosphorus Level

Phosphorus Target

Between 4.0 and 6.00 mg/dl*

25 mg per lb (0.5kg) of cat per day, divided and given with food 2-3 times a day.*

Between 6.0 and 8.0 mg/dl

50 mg per lb (0.5kg) of cat per day, divided and given with food 2-3 times a day.

Between 8.00 and 10.00 mg/dl

100 mg per lb (0.5kg) of cat per day, divided and given with food 2-3 times a day.**

Over 10.00 mg/dl

Discuss with your vet

International

Current Phosphorus Level

Phosphorus Target

Between 1.3 and 1.9 mmol/L*

25 mg per lb (0.5kg) of cat per day, divided and given with food 2-3 times a day.*

Between 1.9 and 2.6 mmol/L

50 mg per lb (0.5kg) of cat per day, divided and given with food 2-3 times a day.

Between 2.6 and 3.25 mmol/L

100 mg per lb (0.5kg) of cat per day, divided and given with food 2-3 times a day.**

Over 3.25 mmol/L

Discuss with your vet

*Not everybody chooses to start binders if phosphorus levels are in this range - most people only start binders once phosphorus levels are over 1.9 (US: 6.0). However, if your cat has previously had high phosphorus levels which you have reduced with binders, or if your cat has high calcium levels, you will probably need to continue to give binders, either at this dosage or even higher, otherwise your cat's values will probably rise over 1.9 (US: 6.0) again.

**I would not give more than 50 mg per lb of cat per day (100 mg per kg of cat per day) without detailed discussions with your vet. It is probably safe, but you need to balance the potential benefits against the possible risks, including the rare possibility of aluminium toxicity - see below. It may be safer to use a smaller amount of aluminium hydroxide together with another binder, such as lanthanum carbonate (Revalzin or Fosrenol).

Aluminium hydroxide does not have to be measured too precisely, but as a rough guide, if you are using powdered aluminium hydroxide, a quarter of a teaspoon of powder contains approximately 300mg of aluminium hydroxide. If you are using a liquid type of binder, as a guide, a teaspoon of Alternagel contains approximately 600mg of aluminium hydroxide.

Here are tables showing approximately how much aluminium hydroxide to give, based on how high your cat's phosphorus level is and how much your cat weighs. It is hard to be specific with the lower doses e.g. if you need to give less than ⅛ tsp, it is going to be tricky to measure, but precise dosing is not essential, so a little bit more or less should not be a problem.

The amounts below are the total daily dose, but the total amount should be divided among as many of your cat's daily meals as possible.

Check phosphorus levels every month to see if any adjustments to your treatment plan are necessary.

Aluminium Hydroxide Binder Tips

Phosphorus binders must be given with food so they can bind with the phosphorus in it. Aluminium hydroxide binders are usually odourless and tasteless if you choose carefully (see below), but since they are a natural (mined) product, they can sometimes add a bit of a gritty texture to food or make it taste a little drier.

See above for recommended dosages. Here are some tips on how to give aluminium hydroxide binders:

Using Aluminium Hydroxide Binders with Canned Food

tablets can simply be crushed and added to the food.

capsules can be opened and the contents mixed with the food.

liquid binders can either be mixed in the food or syringed into your cat's mouth just before eating.

one retailer recommends adding a teaspoon of water to tinned food and letting it stand for ten minutes before serving in order to let the binder mix thoroughly. This may help remove any grittiness.

Using Aluminium Hydroxide Binders with Dry Food

try putting the food in a freezer bag together with the crushed or powder binder and leave them to mingle overnight.

if you are using a liquid binder, you can syringe it into your cat's mouth just before eating.

Aluminium Hydroxide Cautions and Interactions

Side effects
Interactions
Aluminium toxicity
Other concerns

Side Effects

Sometimes phosphorus binders may cause constipation, so watch for this when you first start them and be ready to start a suitable treatment if required.

Interactions

If you are using potassium citrate for metabolic acidosis, give this at least two hours apart from phosphorus binders. This is because products containing citrate can in theory increase the absorption of aluminium, which could increase the risk of aluminium toxicity. Many prescription diets contain potassium citrate, but in most cases, you will not need to use phosphorus binders if you are using a prescription diet.

According to Plumb's Veterinary Drug Handbook, phosphorus binders should be given two hours apart from Baytril an antibiotic. It's probably wise to keep binders away from antibiotics generally.

Plumb's Veterinary Drug Handbook also advises giving phosphorus binders two hours apart from famotidine (Pepcid AC), which is used to treat stomach acid, because it may interfere with the absorption of the treatment, which would make it less effective.

Dr Larry Nagode of Ohio State University has stated that phosphorus binders should be separated from ACE inhibitors such as benazepril (Fortekor) for the same reason.

Phosphorus binders should ideally be given separately from iron, because the binders may reduce the absorption of the iron. Drugstore has some information about this interaction.

Medline Plus mentions that Vitamin C may interact adversely with products containing aluminium, such as phosphorus binders. Cats do not need Vitamin C supplements anyway, they can manufacture all the Vitamin C they need themselves.

I don't know if Slippery Elm Bark would interfere with phosphorus binders, as far as I know this has never been studied, but it might be possible in theory. However, if you are adding Slippery Elm Bark to food once or twice a day, I would still mix binders in with that food in the hope that at least some of the phosphorus would be bound.

Aluminium Toxicity

You may have read that there is a risk of aluminium toxicity from the aluminium in aluminium hydroxide medications. This applies in particular to human patients on dialysis (because aluminium is used in the dialysis process) but since cats are not on dialysis, it was not thought to be a concern for cats (or dogs), especially since even in humans it takes years before it becomes a problem, and cats and dogs don't live as long as humans.

Recently, however, there has been increasing concern about the possible risk of aluminium toxicity in cats using aluminium hydroxide based binders. This is partly because of a study which reported on aluminium toxicity in two dogs on binders, Aluminum toxicity following administration of aluminum-based phosphate binders in 2 dogs with renal failure (2008) Segev G, Bandt C, Francey T & Cowgill LD Journal of Veterinary Internal Medicine 22(6) pp1432-5. There is no abstract available for this study, but Treatment options for hyperphosphataemia in feline CKD: what's out there? (2009) Kidder AC & Chew D Journal of Feline Medicine & Surgery 11(11) pp813-24 reported that the two dogs in question developed "probable aluminum toxicity" after being on binders for only 62 and 65 days. The symptoms seen were "severe neuromuscular abnormalities." The dogs were on dosages of 125mg/kg per day (or 56mg per lb body weight) and 200 mg/kg (or 91mg per lb bodyweight) per day, which is not a particularly high dose.

Obviously these were dogs, not cats, but vets are becoming increasingly aware of the need for caution and awareness when using aluminium hydroxide binders in cats too, particularly when using large doses.

Physical symptoms to watch for include neurological problems, such as stumbling and an awkward gait (although, just to complicate matters, these can actually also be signs of uncontrolled phosphorus levels too, see above). One possible sign of aluminium toxicity is a change in MCV. This is a measure of red blood cell size. If your cat has a low MCV (known as microcytosis), this means the red blood cells are smaller than usual. Although this may simply indicate iron deficiency, it may also be a sign of aluminium toxicity. This sign normally appears before you see physical symptoms, so be sure to monitor your cat's MCV levels.

If you are using potassium citrate for metabolic acidosis, give this at least two hours apart from phosphorus binders. This is because products containing citrate can in theory increase the absorption of aluminium, which could increase the risk of aluminium toxicity. so Many prescription diets contain potassium citrate, but in most cases, you will not need to use phosphorus binders if you are using a prescription diet.

If you think your cat has a problem, I would ask for a referral to a vet school or a neurologist if possible. Chelation therapy plus dialysis have helped remove the aluminium from dogs with aluminium toxicity.

Try not to worry too much. I am not aware of any reported cases in cats to date, and most cases in dogs have occurred in dogs taking over 200 mg/kg. In Updates in feline chronic kidney disease (2008) Dr CL Langston states "Excessive absorption of aluminum can lead to toxicity, including anemia and neurologic symptoms, but this seems uncommon in veterinary practice." In contrast, the dangers of elevated phosphorus control are very real, and very common, and controlling phosphorus is essential for your cat's wellbeing.

If your cat has phosphorus levels that require large amounts of aluminium hydroxide, or if you cannot control your cat's phosphorus levels with aluminium hydroxide only, consider adding another phosphorus binder. Most people in this situation use lanthanum carbonate (Renalzin or Fosrenol). See below for suggestions on dosage.

Other Concerns

If you buy aluminium hydroxide gel or powder in the USA, you may see a warning about arsenic which bizarrely supposedly only applies to people living in California. This is to comply with that state's legal requirements. The fact of the matter is that aluminium hydroxide is a naturally occurring product which is mined, and therefore it contains a naturally occurring tiny amount of arsenic of no more than 8 parts per million. This is no more than you might find in soil or in vegetables grown in soil. However, if you want to be on the safe side, you might wish to avoid inhaling the powder.

If you buy aluminium hydroxide, you may see an expiration date on it. This is usually to comply with pharmacy laws, but in practice, since aluminium hydroxide is a mineral that is mined from the earth, it cannot really expire, so I would not worry too much about expiry dates.

Calcium-Based Binders Back to Page Index

Calcium Acetate
Calcium Carbonate

Ipakitine/Epakitin

Sometimes your vet will recommend using a calcium-based antacid such as Tums or PhosLo as a phosphorus binder. These are not an ideal choice because:

these binders are not as effective as binders containing aluminium hydroxide;
they may make your cat's calcium levels rise too high (hypercalcaemia).

Hypercalcaemia in cats (2001), a paper by Dr Chew presented to the World Small Animal Veterinary Association World Congress 2001 mentions that using calcium-based binders may cause hypercalcaemia. Thus, if you are using a calcium-based binder, frequent monitoring of blood calcium levels is essential. You should not use a calcium-based binder if your cat is taking calcitriol.

Calcium Acetate

The calcium acetates (e.g. PhosLo) bind about three times as much phosphorus as calcium carbonate (e.g. Tums). On the other hand, they are more likely to cause hypercalcaemia.

Calcium Carbonate

The risk of hypercalcaemia is lower with calcium carbonate based binders such as Tums, though it still exists. However, in some cases it may be worth considering using a calcium carbonate based binder called Ipakitine (Epakitin in the USA).

Ipakitine/Epakitin

Ipakitine (known as Epakitin in Canada and the USA) is a combination of a calcium carbonate based phosphorus binder and an oral adsorbent. Adsorbents are products that bind with something else, and adsorbents used in the treatment of CKD usually bind with toxins, thus improving wellbeing. Phosphorus binders are an obvious example of an oral adsorbent, but Ipakitin contains another type of adsorbent too, chitosan, which is said to help with uraemic toxins. There is more information about Ipakitine, including its adsorbent properties, on the Treatments page.

In the marketing literature, emphasis seems to be placed on Ipakitine's role as a phosphorus binder, but many vets seem to sell it to clients whose cats do not have elevated phosphorus levels, so they are presumably advocating it for its chitosan-related effects. It is only supposed to be given for six months, but I have heard of cats who have been on it for longer with no obvious problems.

My own vet in the UK has seen falls in creatinine and BUN (urea) in some cats when using Ipakitine and no other treatments. I did use it myself for Ollie, who did not have very high phosphorus levels, nor were his calcium levels elevated.

For a cat with higher phosphorus levels (over 2.25 international, 7 USA), I personally would opt to use an aluminium hydroxide binder instead of Ipakitine. Even for cats with lower phosphorus levels, if the cat's phosphorus multiplied by total calcium is higher than 70 in US values or 5 in international values, the cat is at risk of tissue calcification (see secondary hyperparathyroidism). In such a case, again I would opt for using an aluminium hydroxide binder in order to get the phosphorus levels under control as quickly as possible.

Effects of an intestinal phosphorus binder on serum phosphorus and parathyroid hormone concentration in cats with reduced renal function (2008) Brown SA, Rickertson M & Sheldon S International Journal of Applied Research in Veterinary Medicine 6(3) pp155-160 reports on a small randomised placebo-controlled study (partly funded by the manufacturers) of twelve cats without naturally occurring renal failure, which indicated that Epakitin appeared to reduce phosphorus levels in the cats, who were fed a commercial (non-prescription) diet and who were in IRIS Stages 1 and 2.

See below for stockists.

Other Types of Binder Back to Page Index

Lanthanum carbonate: Renalzin or Fosrenol

Sevalamer hydrochloride: Renagel or Renvela

Lanthanum Carbonate

New binders are coming on the market in which the active ingredient is lanthanum carbonate. This is supposed to bind more effectively with phosphorus than either aluminium or calcium, and is tasteless. Some people are using Renalzin in addition to aluminium hydroxide when they cannot control phosphorus levels with aluminium hydroxide alone.

See below for dosing if using lanthanum carbonate in addition to aluminium hydroxide because you cannot control phosphorus levels with aluminium hydroxide alone, or if you would prefer not to use really high amounts of aluminium hydroxide.

Renalzin

In October 2008 a binder containing lanthanum carbonate known as Renalzin was released in Europe for the feline market. Initially it was available in UK, Germany, Austria and Benelux, but it is now also available in a number of other countries.

Renalzin contains Vitamin E and kaolin as well as lanthanum carbonate. The vitamin E is intended to act as an antioxidant, and the kaolin as a "toxin binder", by which I think they mean an oral adsorbent. Kaolin (which is often used to treat diarrhoea) can be constipating, so it seems an unusual choice of ingredient, but I suspect Bayer are jumping on the Ipakitine/Epakitin bandwagon here by wanting to add an oral adsorbent. Renalzin also contains the preservative Methyl 4-hydroxybenzoate (E218). This additive is apparently banned in France and Australia, which may explain why the product has not yet been launched in those countries, though I have heard from one person in France who was able to obtain it.

Renalzin is produced in pump form and one dose provides 1 ml, which contains 200mg of lanthanum carbonate. It can be sprayed directly onto food, and makes canned food quite creamy. Renalzin is supposed to be odourless and tasteless but one user in Germany has reported that it tasted slightly bitter and mouldy to her.

Bayer recommend that two pumps (2ml) a day are used, giving a total dose of 400mg of lanthanum carbonate each day. This compares with the recommended human starting dose for Fosrenol (which also contains lanthanum carbonate) of 750-1500mg a day, so the recommended feline dose seems relatively high. However, veterinary sources have stated that lanthanum carbonate can be dosed in the same way as aluminium hydroxide, in which case 400mg is within normal levels. The product on sale in Germany says that two pumps (2ml) a day should be mixed with dry food or three pumps (3ml) a day with tinned food. I have no idea what you are supposed to do if you are feeding both dry and tinned, perhaps average it out.

It is not essential to give Renalzin only twice a day, the total daily dose can be calculated and spread over all meals if required. Phosphorus levels should be checked after 2-4 weeks and the dose adjusted as required. Like Ipakitine/Epakitin, Renalzin is supposed to be given for up to six months only, but most CKD cats have an ongoing requirement for phosphorus control.

Renalzin is not absorbed into the digestive tract like aluminium hydroxide based binders, and therefore should have fewer possible interactions with other treatments. The most common side effects for humans taking lanthanum carbonate are nausea, vomiting and diarrhoea, and I have also heard of CKD cats who developed nausea and vomiting whilst taking Renalzin. The manufacturer confirmed to one person's vet that these were possible side effects.

Some people are using Renalzin in addition to aluminium hydroxide when they cannot control phosphorus levels with aluminium hydroxide alone, or if they would prefer not to use really high amounts of aluminium hydroxide. See below for dosing if using Renalzin in this way.

See below for stockists.

Renalzin is the UK website for Renalzin.

Renalzin: the new innovation for CRF is a video presentation from Bayer about Renalzin.

Safety and efficacy of Lantharenol (Lanthanum carbonate octahydrate) as a feed additive for cats according to Regulation (EC) No 1831/2003 is a European Food Safety report on the basis on which Renalzin was approved. This refers to a number of supporting studies but the majority of these have not been published yet.

Fosrenol

Although Renalzin is not currently available in the USA, a human version of lanthanum carbonate called Fosrenol has been available in the USA since 2005 which is gradually being used in cats. A prescription is required. Fosrenol comes as extremely expensive tablets which are supposed to be chewed, but in order to use them for cats, most people crush the tablets.

Fosrenol dosing is the same as for aluminium hydroxide. So, for example, if you are giving 300mg of aluminium hydroxide a day but want to switch to Fosrenol, you would still need to give 300mg per day.

If you are having trouble getting phosphorus under control using aluminium hydroxide alone, you can use Fosrenol in addition to the aluminium hydroxide. In such cases, a suitable starting dose might be 50-100mg per kg of cat per day, which equates to 25-50 mg per lb of cat per day. You can go up to 200mg per kg of cat per day (just under 100mg per lb of cat per day) if necessary, but obviously work with your vet on determining the most appropriate dosage for your cat.

The most common side effects for humans taking lanthanum carbonate are nausea, vomiting and diarrhoea.

See below for stockists.

Fosrenol - the manufacturer's (Shire's) website.

Eurek Alert has a press release regarding the approval process for Fosrenol in the USA.

Renalan

Renalan is another lanthanum-based phosphorus binder which is currently undergoing testing on cats. It is not yet commercially available.

Form 10-K (2007) of Altair Nanotechnologies Inc has information on the testing of Renalan (pages 16-18), and states that the process to seek regulatory approval was to begin in 2008.

Sevelamer Hydrochloride: Renagel and Renvela

Renagel (sevelamer hydrochloride) is a relatively new phosphorus binder approved for use in humans, with not much history of use in cats. One possible problem is interference with blood clotting, so it may be necessary also to give your cat Vitamin K. It is also very expensive, but may be worth considering if you cannot use the other types of binders for some reason. Doctor's Guide has information on the approval of Renagel for use in the USA.

Renvela (sevalamer carbonate) is the next generation version of Renagel which contains a carbonate buffer. It is intended to help with bicarbonate levels, but in some cases it might actually worsen metabolic acidosis.

Where to Buy Phosphorus Binders Back to Page Index

USA
UK
Canada
Australia and New Zealand

Please read above about which binder to use and why.

Sources - USA

If you buy your binders from your vet, you will often be offered AlternaGel, but this is peppermint flavoured, which most cats hate. AlternaGel also contains potassium citrate.

Another product which vets sometimes stock, Amphojel, comes in both unflavoured and peppermint flavoured version, so check before you buy that you will be getting the unflavoured one; most vets only seem to stock the peppermint-flavoured version.

Most people on Tanya's CRF Support Group use the loose aluminium hydroxide in gel or powder form available from the pharmacies below, or some local compounding pharmacies may be able to order it for you. The loose aluminium hydroxide gel or powder is odourless and tasteless, so is much easier to give. There are three main generic brands available, Spectrum, Gallipot and PCCA. You may be told that a prescription is required, but this is not correct, it is an over the counter product. It may take a local pharmacy a few days to obtain it for you; it is fine to wait that long.

Aluminium Hydroxide

Thriving Pets in the USA sells 500g (1.1 lbs) of aluminium hydroxide dry gel for US$43 plus shipping. They also sell 1 oz at a time (which costs about US$7 including shipping within the USA), as well as capsule or liquid (oral) formulations. If you enter the word "tanya" (without the ") in the promotional code box, you will receive a 10% discount on orders over US$55. Shipping is free for orders over US$55 after the discount.

Drugstore sells AlternaGel for US$8.49 for 12 fl oz, but remember, this is mint flavoured, which most cats dislike.

Fosrenol

Thriving Pets sells nine Fosrenol 500mg tablets for US$45 or ten 1000mg tablets for US$89.95. A prescription is required.

If you enter the word "tanya" (without the ") in the promotional code box, you will receive a 10% discount on orders over US$55. Shipping is free for orders over US$55 after the discount.
My Online Vet sells Renalzin for £22.27 for 150ml, but you would not have to pay the VAT of 17.5% if you were having it shipped to the USA. You would probably end up paying around US$50, but e-mail them to check.

Epakitin

Entirely Pets sells Epakitin for US$15.99 (50g), US$43.99 (150g) or US$64.99 (300g).
Medi-Vet sells Epakitin for US$20.89 (50g), US$46.99 (150g) or US$77.89 (300g).

Sources - UK

Aluminium Hydroxide

Alucaps are an odourless and flavourless phosphorus binder made by 3M. Members of Tanya's CRF Support Group in the UK have successfully obtained Alucaps from Boots, Lloyds and Superdrug during 2011. In May 2011 they cost £8.22 for 120 capsules of 475mg aluminium hydroxide from Boots. Don't say they are for a cat, or they may ask for a prescription from your vet, whereas if you buy them for your own indigestion, they are over the counter. When I asked for Alucaps in Boots, the pharmacist had never heard of them, but - unbeknownst to her - she did actually have some in stock; so you may need to be persistent or ask for them to be ordered for you. If they need to be ordered, they should only take a couple of days to arrive, and it is fine to wait that long.

Thriving Pets in the USA sells 500g (1.1 lbs) of aluminium hydroxide dry gel for US$43, and will ship to the UK and elsewhere. They also sell 1 oz at a time, as well as capsule or oral forms. Contact them to obtain a quote for shipping & handling costs. If you enter the word "tanya" (without the ") in the promotional code box, you will receive a 10% discount on orders over US$55.

Renalzin

Vet UK sells Renalzin for £6.56 for 50g or £17.51 for 150g.
My Online Vet sells Renalzin for £22.27 for 150ml.

Ipakitine

Best Pet Pharmacy sells Ipakitine for £8.92 for 50g or £18.40 for 150g.
Vetscriptions sells Ipakitine for £9.49 for 50g or £21.99 for 150g.

Sources - Canada

Aluminium Hydroxide

Pet Pharm sells an aluminium hydroxide based binder called Basaljel made by Axcan Pharma Inc. It comes in gelcaps, each containing 500 mg of aluminium hydroxide, and they cost CAN$20.16 for 100. Basaljel is also available over the counter in many Canadian pharmacies.

Canada Drugs sell a liquid aluminium hydroxide product called Alugel for CAN$18.16.

Xenex Laboratories in Canada sells 500g of aluminium hydroxide, you can contact them to check the current price, but for reference in June 2011 one member of Tanya's CRF Support Group paid CAN$66 plus CAN$20 shipping, whilst another paid a total of CAN$78 including shipping (she lived closer).

Thriving Pets in the USA sells 500g (1.1 lbs) of aluminium hydroxide dry gel for US$43, and will ship to the UK and elsewhere. They also sell 1 oz at a time, as well as capsule or oral forms. Contact them to obtain a quote for shipping & handling costs. If you enter the word "tanya" (without the ") in the promotional code box, you will receive a 10% discount on orders over US$55.

Fosrenol/Renalzin

Thriving Pets sells nine Fosrenol 500mg tablets for US$45 or ten 1000mg tablets for US$89.95. A prescription is required.

If you enter the word "tanya" (without the ") in the promotional code box, you will receive a 10% discount on orders over US$55.
My Online Vet sells Renalzin for £22.27 for 150ml, but you would not have to pay the VAT of 17.5% if you were having it shipped to the USA. You would probably end up paying around US$50, but e-mail them to check.

Sources - Australia and New Zealand

Your best bet is Alu-Tabs. These are made by Douglas Pharmaceuticals of New Zealand. They come in 600mg tablets rather than a powder, but I imagine you could crush them. They should be available over the counter in pharmacies, though your pharmacist may not realise they are there. Don't say they are for a cat, or they may ask for a prescription from your vet, whereas if you buy them for your own indigestion, they are over the counter.

Home Pharmacy sells 100 Alu-Tabs for AUS$26.99 (I do not know anybody who has used this pharmacy as yet).

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This page last updated: 11 November 2011

Links on this page last checked: 16 January 2010