Pharmacokinetics of tacrolimus granules in pediatric de novo liver, kidney, and heart transplantation: The OPTION study

: Tacrolimus granules were developed for patients who are unable to swallow capsules. Therapeutic drug monitoring (TDM) is required to optimize efficacy and safety, which is based on Ctrough for tacrolimus capsules. Pharmacokinetic (PK) data for tacrolimus granules are required to establish the basis for TDM in those who are unable to swallow capsules. In this phase IV study (NCT01371331) of children undergoing liver, kidney, or heart transplantation, patients received tacrolimus granules 0.15 mg/kg twice daily; first dose was administered within 24 hours of reperfusion. PK analysis samples were collected after reperfusion, after first dose of tacrolimus (Day 1), and at steady state (Day 7; >4 days stable dose). Of the 52 transplant recipients enrolled, 38 had two evaluable PK profiles. Mean AUCtau after first dose of tacrolimus was 211, 97, and 224 hour*ng/mL in liver, kidney, and heart transplant recipients, respectively; corresponding mean AUCtau at steady state was 195, 208, and 165 hour*ng/mL. Ctrough and AUCtau were positively correlated after first dose of tacrolimus and at steady state (Pearson's coefficients: r = 0.81 and r = 0.87, respectively). This study demonstrated that Ctrough is a reliable marker for TDM in pediatric transplant recipients treated with tacrolimus granules, consistent with TDM for other tacrolimus formulations.