There is no consensus on Thymoglobulin (TMG) dose used for induction immunosuppression (IS) in pediatric kidney transplants (KTx). We aimed to identify: 1) TMG induction dose variation 2) whether a lower TMG dose provides safe and effective IS compared to a higher TMG dose.

We performed a retrospective analysis of all first time pediatric KTx pts (age <21 yo) in the NAPRTCS registry since 1998 on contemporary MMF and tacrolimus based IS with TMG induction. An a priori cut-off of 7.5 mg/kg cumulative TMG dose was used to identify low (<7.5 mg/kg) and high (= or >7.5mg/kg) exposure groups. Primary outcome was time to first acute rejection episode. Secondary outcomes included graft function, survival, hospitalizations due to infections, and time to first PTLD episode.

455 pts met inclusion criteria (59% male, 49% Whites, 26% Blacks, 38% Living donor source, 36% ESRD due to CAKUT, 19% due to NS/FSGS, 15% due to GN). Median age at KTx of 13 years and 67.5% transplanted in the past decade after 2005. For the entire cohort, the median cumulative TMG dose was 6.8 mg/kg (range 0.8-23.8) with a median of 5 doses (range 1-20) and a median 1.5 mg/kg/dose (range 0.4-3.1) introduced at a median of 0 day post op (range 0-15).

64% received <7.5 mg/kg total TMG and the rest received 7.5 mg/kg or more. There was no difference in age at KTx, gender, race, ESRD etiology, or HLA mismatch between groups. However, a higher proportion of low dose group was transplanted in past decade, and delayed graft function was significantly higher in high dose group (18% vs 6%, p <0.001).

Time to first acute rejection was similar in both groups (Kaplan-Meier Estimates with log-rank p-value 0.07). There was no significant difference in graft or patient survival, or time to PTLD. Hospitalization for infection rates was similar at 6 and 12 months. The low dose group had better graft function at 6 and 12 months by 3-4 ml/min/1.73m2 (p value 0.03).

We conclude that wide variation exists in TMG induction dose with more than third pediatric KTx recipients receiving cumulative dose of 7.5mg/kg or greater. This data suggests a smaller dose < 7.5 mg/kg may provide effective and safe IS compared to a higher TMG dose, though the higher dose group may have been at higher immunologic risk.

CITATION INFORMATION: Ashoor I, Martz K, Beyl R, Dharnidharka V. Reassessing Thymoglobulin Induction in Kidney Transplantation (RETHINK): An Analysis of the North American Pediatric Renal Trials and Collaborative Studies (NAPRTCS) Registry. Am J Transplant. 2017;17 (suppl 3).

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