Epogen is the brand name for a synthetic version of erythropoietin.

Erythropoietin is a hormone which is necessary to stimulate the bone marrow to produce red blood cells. Since it's produced by the kidneys, when kidney function drops below a certain point, anemia sets in. This usually does not represent a significant factor until late middle stage crf. In Coco's case, she was started on Epogen after being on sub-q's for almost 2 ½ years, with a PCV of about 22%. Many vets prefer to wait until the PCV has dropped lower, between 12% and 18%.

Epogen is not appropriate for all anemias, all other possible causes (deficiences, auto-immune, etc.) should be treated and resolved first. It's a specific treatment for the anemia caused by deteriorated kidneys, and is fully effective. It simply substitutes for the erytropoietin that would be produced normally.

There is a downside that can occur in some cats, which is why it is prescribed only when needed, and monitored closely. Since Epogen (and Procrit, a competing brand) are synthesized from HUMAN rather than feline DNA, some cats may eventually recognize it as foreign protein, and develop antibodies against it. If antibodies are formed, they not only impede the function of the Epogen, but also whatever natural erythropoietin is still being produced by the kidneys.

Not all cats develop these antibodies (current estimates are 30% or less), and for most cats needing Epogen treatment the potential risk should not be taken as a factor in the decision-making process. Most cats needing Epogen would die without it before the time antibodies could form, so it's academic. I've heard of at least one cat that continue on Epogen for over 4 years without problems, vs only one or two instances of anibody formation that I recall being reported on this list.

It's an important part of the treatment, however, to do regular hematocrit testing. This is done both to monitor the raise in PCV for the purposes of dosage frequency adjustment, and to be alert to the formation of antibodies, signaled by a sudden drop rather than a rise in the PCV.