Therapy
This chapter will provide you with a basic understanding of the management of chronic kidney disease in cats and then present the International Renal Interest Society (IRIS) treatment recommendations by stage.
The aim of CKD treatment is to prolong the cat’s life while maintaining a good quality of life. In detail, this means:
- Identify the cause of CKD and eliminate or treat it as far as possible.
- Stabilise renal function and slow progression to prolong the life of the cat.
- Ameliorate the associated diseases or symptoms (clinical signs) of CKD to improve the cat’s quality of life.
Identifying and eliminating the causes of CKD can be challenging and is often unsuccessful. It is therefore even more important to ensure that medication is not harmful to the kidneys, as can be the case with some painkillers, antihypertensives, antibiotics and anaesthetics.
The more advanced the CKD, the greater the treatment focus on improving quality of life. Due to the increasing number and severity of clinical symptoms, the focus is on the later stages.
The vicious cycles of kidney destruction cause the kidney to lose more functional nephronsNephrone sind die Filtereinheiten der Nieren...., so the kidney’s performance continues to decline. Although it is not possible to stop these vicious cycles, it is possible to slow them down to prolong the cat’s life.
Phosphate reduction
Reduced kidney function results in too much phosphate remaining in the body, leading to an excess of phosphate which, together with a hormonal imbalance, leads to increased bone resorptionThe re-uptake of substances from tissues, in particular bone, into the blood. It should not be confused with absorption, the initial uptake of substances into the body, for instance from food in the intestines, through the lungs and via the skin. Reabsorption, in contrast, occurs.... Calcium and phosphate are released from bone. Excess phosphate is then stored with calcium in the kidneys, leading to kidney calcification, which further reduces the number of functioning nephrons. As a result, chronic kidney disease progresses.
Phosphate reduction is therefore a key treatment intervention in CKD. The initiation of therapy in early IRIS is based on FGF-23 levels and in late IRIS on blood phosphate levels (see below).
As cats absorb phosphate from their diet, one approach is to reduce phosphate. There are basically two ways of doing this, which can be used separately or in combination.
A. Renal diets contain less phosphate than standard diets. The reduction in phosphate is achieved by replacing phosphate-rich animal proteins, such as muscle and offal, with vegetable proteins (e.g. wheat gluten). Vegetable proteins contain less digestible phosphate for the cat. At the same time, most kidney diets are also protein-reduced, so there is even less phosphate in the diet. Products containing flavour enhancers (e.g. sodium diphosphate), including snacks, should be used with caution. These additives do not have to be declared, but can contain a lot of phosphates.
Replacing animal protein with vegetable protein is not equally palatable to all cats. As carnivores, cats like the smell of animal protein and therefore need to be carefully introduced to some kidney diets.
There are now a large number of kidney diets available, so it is a good idea to test which one your cat likes to eat. Many senior diets are already phosphate-reduced.
Extremely phosphate-reduced kidney diets are almost unpalatable to cats because the protein would have to be reduced even further. Therefore, in the later stages of IRIS, the combination of a renal diet and a phosphate binder is usually essential.
B. Phosphate binders are substances that absorb phosphate in the gut and then excrete it in the faeces. Only lanthanum carbonate is currently approved for use in CKD cats in the EU.
Lanthanum carbonate forms insoluble complexes with phosphate from the feed in the stomach and intestines, which are then excreted in the faeces. As a result, phosphate cannot be absorbed into the blood.
It is best to give the phosphate binder directly with the food at mealtimes. If the cat eats more than one meal a day, it makes sense to divide the daily dose of phosphate binder between the number of meals.
Unlike renal diets, lanthanum carbonate can generally be dosed as needed to lower blood phosphate levels. Renal diets are usually limited in their ability to lower phosphate levels in the later stages of IRIS, so phosphate binders must be given in addition to renal diets, especially if the cat is not eating all of its renal diet and must be fed other foods.
As all phosphate binders can reduce the absorption of medicines to varying degrees, it is advisable to give medicines 1 hour before or 3 hours after taking a phosphate binder.
Phosphate binders containing calcium carbonate should be used with caution in CKD cats as they may increase the tendency for kidney calcification. They usually also contain chitosan, which can also bind non-specific drugs, fats, enzymes, cells, important dietary components, and more. Calcium carbonate-based products have been around for more than 20 years. Until there was an approved phosphate binder, they were the only ones that could be used. However, they have not been adequately tested (efficacy and toxicity studies) and are not approved for use in CKD, but may actually only be used in healthy cats. Lanthanum carbonate showed no adverse effects in 10-fold overdose studies.
IRIS Recommended Phosphate Levels per Stage & FGF-23 Blood Concentration
Specifically, the IRIS recommends phosphate reduction if the following serum phosphate levels are exceeded per stage or if the FGF-23 level is above 400 pg/ml, especially in the early stages
Protein Reduction
The protein content of food is reduced to lower levels of uraemic toxinsToxic, nitrogen-containing urinary substances responsible for uraemia and kidney damage..... In the intestines, bacteria generate the precursors of uraemic toxin from proteins. These are then absorbed and converted into actual uraemic toxins in the liver. These need to be excreted by the kidneys. However, reduction of protein in food as a therapeutic option is disputed, as cats depend on protein as an energy source (see: cats as obligatory carnivores). A better approach is to eliminate factors that trigger uraemiaA raised level in the blood of urea and other urinary substances, which in chronic kidney disease can no longer be adequately excreted due to impaired renal function (glomerular filtration rate). This leads to renal damage due to uraemic toxins, toxic urinary substances The symptoms... (accumulation of uraemic toxins in the blood) and thus symptoms at an early stage by binding their precursors already in the intestines. In principle, it is naturally also better for the kidneys if less urinary substances are excreted, and this can be supported, for example, by the use of oral dialysis to lower levels of uraemic toxins.
Reduction of blood pressure
The kidneys are organs that can regulate their own blood pressure (“autoregulation” of kidney blood flow). They have a variety of mechanisms at their disposal to help them do so. The filtration rate of individual nephrons is dependent on blood pressure. The rate increases with higher blood pressure. However, persistent high blood pressure can also harm the kidneys. It results in overburdening and hardening of the blood vessels (sclerosisThe hardening of an organ or tissue caused by a replacement of normal tissue with connective tissue. Sclerotic tissues and organs are less elastic....), due to the lack of protective substances. This leads to progressive damage of the vascular system of the nephrons and eventually to their destruction. Twenty per cent of CKD cats develop high blood pressure at an early stage. However, there are indications that this figure is actually much higher.
High blood pressure can lead to a variety of clinical symptoms: central nervous disorders such as seizures, cramps, lethargy, strokes, difficulty in walking, visual disturbances, and even blindness due to a retinal detachment.
High blood pressure also leads to an increase in proteins in the filtrate, and these can no longer be reabsorbed, leading to increased protein in the urine (proteinuriaIncreased protein in urine, leading to loss of protein. Normally, only a very small amount of protein is excreted in the urine. In chronic kidney disease, the amount lost may increase. High blood pressure damages blood vessels in the nephrons making them more permeable and...). CKD progression can be slowed down by reducing blood pressure and, with it, proteinuria.
Reduction of proteinuria
As proteinuria is usually caused by high blood pressure, proteinuria and high blood pressure can be reduced together (it is important, however, to establish that the cause of the proteinuria are really the kidneys). To do so, cats are given targeted medication, usually in food as tablets or as liquid suspensions.
Reduction of individual symptoms
The symptoms of CKD vary from cat to cat and need to be treated individually. Reducing uraemia and blood pressure, alone, can improve many symptoms.
It’s critically important, in spite of nausea, vomiting and loss of appetite, that your cat eats well. You should try and improve the attractiveness of food, for instance by warming it up and serving small portions several times a day. If your cat’s appetite doesn’t improve, medicines that stimulate appetite and/or reduce stomach acid can also help.
To encourage your cat to drink, provide it with a choice of fresh water sources, possibly including a fresh water fountain, or add a few drops of tuna oil to the water to make it more appealing.