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 Epogen for Cats
One of the many things the kidneys do is to regulate how many red blood cells are circulating. This makes sense, because the kidneys filter the entire blood volume many times a day and are in an excellent position to keep track of stuff like that. When the kidneys decide that there needs to be more red blood cells, they release a hormone called erythropoeitin. The erythropoeitin is carried by the blood, and when the bone marrow detects it, the marrow produces more red blood cells.
When the kidneys fail, one of the functions that fails is the production of erythropoeitin. With low levels of this hormone in circulation, the patient's red blood cell count drops to abnormally low levels. This is called anemia.
We measure the number of red blood cells in two ways. The simplest is by a lab value called Packed Cell Volume, or PCV. Simply put, blood is made up of two things, the cells, and the fluid. Normally, about 40% of the blood is cells and 60% is fluid. To measure this, we put blood in a thin tube, plug one end, and spin it in a centrifuge. Spinning the tube simulates much higher gravity, and the heavier cells settle to the bottom  quickly. We then simply measure the relative proportions of cells to fluid.
When the number of red blood cells goes down, the PCV drops. Normally, cats run about 30 to 45. When cats get down to below 20, it is time to consider starting treatment.
Treatment consists of giving extra erythropoetin. There is product called Epogen or Procrit that is made for humans. It is pure recombinant human erthropoetin, which means that it is an exact copy of the human version of erythropoetin. It is made by transplanting the human gene into a bacterium. Although cat erythropoetin is slightly different than the human version, it is apparently close enough, because it works to stimulate cat red blood cell production.
However, because human erythropoetin is slightly different than cat erythropoetin, some cats will treat it as a foreign invader, just like a transplanted kidney, and make antibodies against it. Some studies report that this happens in as many as 30% of cats. At best, this renders further treatment futile. At worst, it can rarely cause an irreversible worsening of the anemia problem, even resulting in death.
Most clinicians believe that it is better to treat severly anemic cats than to not treat despite the risks. Although reactions to erythropoetin do seem to happen in as many as 30% of the cats we treat, the reaction is often mild, and with appropriate monitoring no lasting harm is done. It is important to realize, however, that a real, albeit small, risk of serious adverse events exists.
The latest treatment protocol calls for injections once a week. At the time of the first injection, supplementary vitamins and minerals are given as well, and are repeated once a month as needed. The PCV must be checked weekly at each injection to watch for the development of adverse reactions. Once the PCV reaches 28 or so, we usually stop injections and monitor PCV once a month, giving an injection whenever the PCV drops again.
Erythropoetin comes in a vial that holds 2000 units. We give about 50 units per pound each dose, so most cats get about 250 units (for 5 pounds of bodyweight) to 500 units (for 10 pounds of bodyweight), making a bottle last for 4 to 8 doses. We are unable to sell the drug by-the-dose, so a client must buy a whole vial at a time for their cat. A vial costs about $80. It costs around $15 to $25 per visit for a PCV measurement, vitamin injection if needed, and the erythropoetin injection, not including the cost of the erythropoetin.
Many cats in renal failure have been helped by erythropoetin injection. Used cautiously and monitored well, it can safely provide increased vitality and energy for anemic cats.
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