*Purpose: Tacrolimus exhibits interpatient pharmacokinetic variability that impacts clinical responses and requires routine trough therapeutic drug monitoring. Tacrolimus troughs do not consistently predict area under concentration-time curves 0 to 12 hours(AUC_0-12hr) which quantitates therapeutic exposure. To investigate this issue, tacrolimus AUC_0-12hr determined by Non-Compartmental Analysis(NCA) was compared to Robust(9-timed samples) and Sparse (2-timed samples) AUC_0-12hr estimates using Maximum a Posteriori-Bayesian (MAP) Approach in 67 stable KTR.

*Methods: During an open-label single center pharmacology study, 12-hour serial samples were collected to determine steady-state tacrolimus AUC_0-12hr using standard NCA. Robust (9-timed samples) and Sparse (trough and 8-hour samples) generated AUC_0-12hr estimates by MAP Approach using the Advanced Dosing Solutions Program (ADAPT v5) . AUC_0-12hr comparisons were made by paired T-tests with intraclass correlation coefficient(ICC) providing level of agreement between AUC_0-12hr estimates using SAS V9.4. Bland Altman plots compared AUC_0-12hr data.

*Results: 35 Black and 32 White stable KTR(e-GFR=57.1±15.7ml/min/1.73m2) received tacrolimus dose of 3.4±1.7 mg/study with troughs=6.8 ±1.7 ng/ml. The group NCA-AUC_0-12hr was 123.8±33.7 ng∙hr/ml compared to MAP estimates for Robust-AUC_0-12hr =130.2±32.8 ng∙hr/ml and Sparse-AUC_0-12hr of 126.5±33.0 ng∙hr/ml. Summary Table compares tacrolimus AUC_0-12hr with the ICC supporting correlations for MAP- Robust and Sparse estimates to measured NCA for AUC_0-12hr.

*Conclusions: Use of MAP estimation from sparse sampling and trough monitoring post-transplant provides an approach to quantitate tacrolimus AUC_{0-12hr .}

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