This link is from an article from the UK, but here is a history of the rabbit vs. horse preparations. It says ATGAM is administered for 8-14 days, but I thought NIH recommends 4 or 5 days only (my son had 4):
http://www.medicinesresources.nhs.uk...Dec%202012.pdf
"The standard ATG preparation used for the treatment of AA in the UK had been horse ATG (Lymphoglobuline®, Genzyme), however this was withdrawn from the market in 2007 and replaced by rabbit ATG (Thymoglobuline®, Genzyme). Rabbit ATG had previously been used mostly for a second course of immunosuppressive therapy (IST) in patients who had relapsed or were refractory to a first course of horse ATG (2, 3). Thymoglobuline® is licensed in the UK for immunosuppression in solid organ transplantation; it is not licensed for the treatment of AA (4).
Atgam® (another horse ATG preparation) is approved in the US for the management of allograft rejection in renal transplant patients and for the treatment of moderate to severe AA in patients who are unsuitable for bone marrow transplantation (5). For AA the recommended dose regimen is 10-20 mg/kg daily for 8 to 14 days; additional alternate-day therapy up to a total of 21 doses can be administered. Because thrombocytopenia can be
associated with its administration, patients may need prophylactic platelet transfusions to maintain platelets at clinically acceptable levels.
Atgam® is not licensed in the UK but is available on a named patient basis (6)."