*Purpose: Tacrolimus is widely accepted as the mainstay of immunosuppression in solid organ transplant. Inherited differences in CYP3A activity are known to contribute to dosing heterogeneity. Our evaluation assesses the utilization of genetically-guided tacrolimus starting doses on time to therapeutic range in a cohort of kidney transplant recipients.

*Methods: Pharmacogenomic (PGx) panel testing was introduced as a standard of care within the Yale New Haven Health Transplant Center for patients undergoing living donor kidney transplant and waitlist patients expected to undergo transplant within 12 months. Between April 2019 and January 2020, data was collected on 63 patients with PGx testing. At time of analysis, 18 patients had PGx data available prior to kidney transplantation. The control group consisted of 26 patients who were transplanted within the same time period and did not receive PGx testing. A primary outcome of time to 2 consecutive therapeutic tacrolimus troughs was evaluated. Therapeutic trough was defined as a level between 8-10 ng/mL. Secondary outcomes analyzed include recommended initial tacrolimus dose, dose at 30 day post transplant, acceptance rate of genotype guided dose recommendations, number of tacrolimus dose adjustments, and occurrence of supratherapeutic trough levels above 14 ng/mL.

*Results: Pharmacist recommendations for initial tacrolimus dosing based on genotype profile were accepted 50% of the time. The average number of days to 2 consecutive therapeutic tacrolimus troughs was 16.72+9.9 days vs. 16.75+7.3 days in the PGx and no-PGx cohorts respectively (p= 0.99). An average of 3.9 vs. 4.3 dose adjustments were needed to achieve 2 consecutive therapeutic troughs in the PGx vs. no-PGx respectively. There were no significant differences detected between average pharmacist recommended initial doses and average doses at 30 days in the PGx cohort (9.28+2.9 vs. 9.29+5.4, p=0.998). Of the patients in the PGx cohort, 44% had supratherapeutic tacrolimus troughs >14 ng/mL in the 30 day period following their transplant vs. 73% in the no-PGx cohort.

*Conclusions: PGx was used to safely dose tacrolimus in our first cohort of 18 patients with PGx at the time of transplant. Although the pharmacogenomics based tacrolimus dosing did not result in a shorter time to therapeutic trough, the average doses at 30 days were more accurately predicted by pharmacist recommendations for initial dose based on genetic profile. Supratherapeutic tacrolimus troughs were also less common in the PGx cohort despite starting at higher doses.

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