High LJones,
I am a bit late to your question.
AA affects three lines:
red blood cells (hemoglobin)
platelets
neutrophils (a type of white blood cell that fights bacterial and fungal infections)
What are you father's current numbers? That way I can get a better idea of his situation.
ATG-horse/cyclosporine/Promacta (triple therapy) is usually the first-line treatment. It can take a long time for the therapy to work. Every person responds differently. How long your doctor will wait until trying a second-line treatment also depends on several factors: overall health of patient, age, how severe neutropenia/platelets are/other risk factors in waiting. There are cases where it's taken over 2 years for horse-ATG to work. YES -- I am serious!! But it's not wise to wait that long, especially if the patient is transfused (blood and platelets) with very neutrophil levels. Remember: what makes AA most serious is not the need for blood transfusions, but rather the low neutrophils and low platelets that can trigger a medical emergency at any time (infection or serious brain bleed). For the record, no one lets their hemoglobin to get down to dangerous levels once a person is known to have a blood problem. Of course, an AA patient can get iron overload if they are transfused with blood for a few years or more, but that's another story.
Note: If a person has heart issues, low hemoglobin becomes more of an issue, and thus transfusion threshold protocols change.
Here are some second-line treatments for refractory AA (refractory = first treatment didn't work). It's not that the same things as relapsed AA (where first treatment did work for a period of time).
For AA refractory settings, these are your options that I am currently aware of:
1 Rabbit-ATG (instead of horse) + cyclosporine/tacrolimus/sirolimus
2 Campath (Alemtuzumab)
3 High-dose N-Plate (sister drug to Promacta)
4 Danazol/other androgens
5 Drug Trial enrollment
6 Bone Marrow Transplant (your father's age makes this option much less likely, but some doctors will do them under 70, or even 75 (pushing it).
It merits saying that Campath is now preferred to Rabbit-ATG (actually, it's Rabbit-ALG, but they say "ATG", as they do for horse). Why? It's about 10% or more likely to work than rabbit, plus there is no other treatment used alongside it; that means it's a monotherapeutic treatment (no cyclosporine, etc.).
If you have any more questions, please let me know.
May your father go into remission.
Take good care.