Efficacy of combination therapy with anti-thymocyte globulin and cyclosporine A as a first-line treatment in adult patients with aplastic anemia: a comparison of rabbit and horse formulations.

Anti-thymocyte globulin (ATG) is a key drug in immunosuppressive therapy for patients with aplastic anemia. The mainstay of ATG therapy had been a horse ATG (hATG) formulation, Lymphoglobulin or ATGAM, but Lymphoglobulin was recently discontinued, and Thymoglobulin, a rabbit ATG (rATG) formulation, is currently used as the first-line drug in many countries, including Japan. However, a recent randomized clinical trial reported significantly unfavorable outcomes associated with the use of rATG regimens. We retrospectively analyzed clinical outcomes of adult patients with moderate to severe aplastic anemia who were treated with 3.5 mg/kg of Thymoglobulin (n = 22) or 15 mg/kg of Lymphoglobulin (n = 25) in our facility. The estimated overall response rates in the rATG and hATG groups were 64.6 versus 56.0 % at 6 months, and 76.4 versus 69.2 % at 12 months, respectively; and there was no statistical difference between the two groups (P = 0.32). Overall survival at 24 months was not significantly different: rATG 89.8 % versus hATG 96.0 % (P = 0.39). Early phase infection was observed in 37.5 % of cases in the rATG and 14.8 % in the hATG group, but the frequency was not statistically different (P = 0.107). Our data indicate that Thymoglobulin at a dose of 3.5 mg/kg is a viable alternative when hATG is not available.