*Purpose: Rabbit antithymocyte globulin (rATG) is FDA approved for kidney transplant induction therapy and treatment of T-cell mediated rejection (TCMR). While prior studies comparing dosing weight strategies for induction therapy have illustrated similar outcomes between IBW and TBW, there is no data comparing dosing strategies for treatment of rejection. This study was designed to identify the impact of dosing weight on outcomes in kidney transplant recipients treated for TCMR.

*Methods: This was a single-center, retrospective review of kidney transplant recipients who received at least one dose of rATG for the treatment of TCMR between 2014 and 2019 at Northwestern Memorial Hospital. Patients were excluded if they were multi-organ transplant recipients < 18 years of age. Patients were divided into groups based on cumulative rATG exposure of > 7.5 mg/kg or ≤ 7.5 mg/kg according to IBW. The primary outcome was the change in serum creatinine (SCr) from the first dose of rATG to one month after the final dose. Six-month secondary outcomes included graft survival, hospital readmissions, and infection rate. In addition, we evaluated the incidence of leukopenia (WBC < 3.5 K/UL), neutropenia (ANC < 1.5 K/UL), and thrombocytopenia (PLT < 150 K/UL) after the final rATG dose.

*Results: 44 patients who received rATG for treatment of TCMR were included, with 16 patients receiving > 7.5 mg/kg and 28 patients receiving ≤ 7.5 mg/kg. BMI was significantly greater in the group receiving > 7.5 mg/kg group (31.3 vs 25.2 kg/m², p=0.008), with other baseline characteristics similar between groups. There was no difference between groups in the percent change in SCr one month after rATG therapy (-14.3% vs -16.9% p=0.8). Graft failure at six months was numerically higher in the >7.5 mg/kg group; however, this was not a statistically significant finding (31.3% vs 17.9%, p=0.46). There were two fungal infections identified, Cryptococcal meningitis in the > 7.5 mg/kg group and pulmonary blastomycosis in the ≤ 7.5 mg/kg group. One patient died from septic shock in the >7.5 mg/kg group. Overall, the infection rate was similar between treatment groups (43.8% vs 25.0%, p=0.31). No difference was identified for other secondary outcomes (Table 1).

*Conclusions: There was no significant difference in percent change in SCr between dosing groups in kidney transplant patients treated for rejection. There was a trend towards a decreased risk of infectious complications, hospital readmissions, and graft failure in the ≤ 7.5 mg/kg dosing group. Larger, prospective studies are needed to confirm these findings.

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