You can look at the drug insert at this link.
http://www.rxlist.com/cgi/generic/aranesp.htm
John used Procrit, which is basically the same thing, about two years after his treatment. He did not start using it until his reticulocyte percentage reached at least 1.5% because you need to be making a certain amount of red cells in your bone marrow on your own. It acts on the stem cells already committed to the red cell line.
Also, we had his EPO level checked to see how much his kidneys were producing. EPO is body's natural Arenesp. If your EPO levels are over 500, you may not see a response to the drug therapy. But you won't know until you try it and it can take up to 12 weeks before you see a response. Your doctor should monitor your Absolute reticulocyte count and reticulocyte percentage. These are the new red blood cells in your CBC.
Eventually, the procrit stopped being working for his so he discontiued it and remained transfusion free without it.