METHODS: Population pharmacokinetic models of tacrolimus were selected (n=17) for evaluation from a recent systematic review. The models were transcribed and implemented in NONMEM version 7.4.3. Data from 85 heart transplant recipients (2387 tacrolimus concentrations) administered the oral immediate-release formulation of tacrolimus (Prograf®) were obtained up to 391 days post-transplant. The performance of each model was evaluated using (1) prediction-based assessment (bias and imprecision) of the individual predicted tacrolimus concentration of the fourth dosing occasion (MAXEVAL=0, FOCE-I) from 1-3 prior dosing occasions and (2) simulation-based assessment (prediction-corrected visual predictive check, pcVPC). Both assessments were stratified based on concomitant azole antifungal use.

RESULTS: Regardless of the number of prior dosing occasions (1-3) and concomitant azole antifungal use, all models demonstrated unacceptable individual predicted tacrolimus concentration of the fourth dosing occasion (n=152). The pcVPC graphics indicated these models inadequately predicted observed tacrolimus concentrations.