*Purpose: Tacrolimus (Tac) is the cornerstone of immunosuppression used in kidney transplant recipients (KTRs). Tac high variability, low time in therapeutic range and non-adherence are significantly associated with poor long-term outcomes. The influence of converting to once daily, extended-release LCP-Tac on those with high variability in KTR is not well-studied.

*Methods: This was a single-center, retrospective cohort study of adult KTRs converted from Tac IR to LCP-Tac who were at least 1-yr post-transplant. Primary outcomes were to assess tac variability, using the coefficient of variation (CV), measured in trough levels drawn in the ambulatory setting from 3-12 months post-transplant, compared to steady-state levels drawn after conversion to LCP-Tac. High Tac variability was defined as Tac CV >30%. Time in therapeutic range (TITR) was also measured using the modified Rosendaal method. Univariate paired tests were utilized for statistical comparison and inferences.

*Results: There were 193 KTRs included in this LCP-Tac conversion analysis, with a mean follow-up of 3.2±0.7 years and 1.3±0.3 years since conversion. The mean age was 52±13 years; 70% were African American, 39% were female, mean of 4 HLA mismatches, 44% cPRA, 16% living donor and 12% DCD. Tac CV was 29.5% before conversion, which increased to 33.4% after LCP-Tac (p=0.008). In those with Tac CV >30% (n=86), conversion to LCP-Tac reduced variability (40.6% vs. 35.5%; p=0.019) and for those with Tac CV >30% and non-adherence or med errors (n=16), LCP-Tac conversion substantially reduced Tac CV (43.4% vs 29.9%; p=0.026; Top Figure). TITR was similar before and after LCP-Tac conversion for the overall cohort (74.6% vs. 75.2%; p=0.805), while TITR significantly improved for those with high Tac CV with (52.4% vs. 82.8%; p=0.027) or without (64.8% vs. 73.2%; p=0.005; Bottom Figure) non-adherence or med errors. Infection with high Tac CV did not appreciably influence variability or TITR. In the overall cohort, 3% had rejection before conversion and 2% after (p=NS). At end of follow-up, graft and patient survival were 94% and 96%, respectively.

*Conclusions: In those with high Tac CV, conversion to LCP-Tac is associated with a significant reduction in variability and improvement in TITR, particularly in those with a history of documented non-adherence or those prone to medication errors.

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