Introduction: The optimal dosing of anti-thymocyte globulin (ATG) in order to prevent graft rejection, while minimizing the risk of drug-related infectious complications remains controversial.
Methods: In October of 2022, our institution implemented a protocol change transitioning from actual body weight (ABW) to ideal body weight (IBW) based ATG dosing. Isolated adult kidney recipients transplanted in the 6 months prior to and following the protocol change were included in this study. Patients were excluded if they were converted to belatacept or experienced primary graft failure. All patients received a total of 6mg/kg of ATG dosed either by ABW or IBW, with or without IVIG based on the prescence of donor specific antibodies (DSA). ATG was administered over three doses, with each dose rounded to the nearest 25mg vial size. Tacrolimus and mycophenolate mofetil were started on post-operative day (POD) 0, while corticosteroids were tapered based on immunologic risk and comorbidities.
Patients were followed prospectively from the date of transplantation until 6 months post-transplant or graft failure. The primary outcome for this study was biopsy proven acute rejection (BPAR) within 6 months. Additional secondary endpoints included: absolute lymphocyte count on POD 7, serum creatinine at 6 months, and hospitalization for infection. Chi-square or Fisher’s test of independence were used to compare categorical variables between ABW and IBW groups, while continuous variables were analyzed using the Student’s T-test.
Results: A total of 105 patients were included in the ABW group and 107 patients in the IBW group. The mean age was 53.4 years in both groups, with diverse racial representation. The primary causes of end-stage kidney disease were hypertension (37%) and diabetes (20%), and 14 patients had a diagnosis of HIV. Living donors comprised 32% of transplants (34% ABW vs 31% IBW), and 16% of patients in each group had preformed DSA >2,000. Rapid steroid withdrawal occurred in 58% of patients in the ABW group and 63% of patients in the IBW group.
The mean total dose of ATG administered was 428.3±85.8 in the ABW group and 386.7±58.5 in the IBW group (5.9mg/kg vs 5.2mg/kg actual body weight; p<0.01). At the conclusion of the study, 4 episodes of BPAR had occurred in the ABW group compared with 5 in the IBW group (p=1.00). The absolute lymphocyte count (289 vs 318; p=0.49) and serum creatinine (1.4 vs 1.4; p=0.43) were also not statistically different between the groups; however, a lower incidence of hospitalization for infection was observed in the IBW group (15% vs 34%; p=0.10).
Conclusion: No significant change was observed in the incidence of BPAR within 6 months of kidney transplantation following a change in our institutional protocol for ATG dosing, but a lower incidence of hospitalization for infection was observed with IBW based dosing. Additionally, an average cost savings of 1,189$ per patient was realized over the course of ATG induction.