Purpose: To determine the effect of attaining early therapeutic tacrolimus (TAC) trough concentrations on biopsy-proven acute rejection (BPAR) within 12 months post-transplantation in adult kidney recipients receiving alemtuzumab induction, mycophenolate, and steroid-free regimen.

Methods: TAC levels were retrospectively collected from 327 recipients from 2009 to 2014. Exclusion criteria were second transplant, thymoglobulin or basiliximab induction, and cyclosporine or sirolimus use within 6 months post-transplantation. Time points included day of discharge, week 1-4, and month 3, 6, and 12. Recipients were divided into two groups: those with at least one episode of BPAR and those without BPAR. Target TAC levels were 8-10 ng/mL at 0-4 months and 6-8 ng/mL at 5-12 months.

Results: Recipients meeting criteria with at least one episode of BPAR (n=28) and without BPAR (n=190) had similar demographics, except for Caucasian ethnicity (25% BPAR vs 54.2% no BPAR; p=0.01) and focal glomerulosclerosis etiology (32.1% vs 14.8%; p=0.02). Time to discharge was 6 ± 3 days. BPAR episodes within 12 months (median 5.3; range 3.8-9.9 months) were 6.9% (n=15). Mean TAC level within 30 days prior to first BPAR episode for the first 12 months was 6.3 ± 2.7 ng/mL. Mean TAC levels were significantly different between BPAR and no BPAR recipients on day of discharge, week 1, and week 4 and reached target level by week 2 (Table 1). Mean TAC levels had no association with the incidence of opportunistic infections or urinary tract infections at any time points.

Conclusion: Early mean TAC levels in both groups were below the recommended target range. This suggests alemtuzumab has a protective effect on acute rejection within the first 12 months post-transplantation despite subtherapeutic TAC levels within the first 2 weeks. Discharging recipients post-transplant prior to reaching target TAC level does not appear to impact acute rejection.

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