Adding sirolimus to tacrolimus-based immunosuppression in pediatric renal transplant recipients reduces tacrolimus...

In adult renal recipients, coadministration of tacrolimus (TAC) and sirolimus (SIR) results in reduced exposure to TAC at SIR doses of 2 mg/day. Eight pediatric renal recipients (median age at transplant 2.0 years, range: 1.2-12.9 years) were converted to TAC- and SIR-based immunosuppression as a rescue therapy. All patients had biopsy-proven chronic allograft nephropathy. TAC levels were measured using a commercially available EMIT assay and SIR levels with a newly developed assay based on the LC-MS MS technology. SIR was started at 0.13+/-0.05 mg/kg/day (3.51+/-1.26 mg/m2/day) in two divided doses. TAC was given at 0.14+/-0.09 mg/kg/day, resulting in a trough level of 6.3+/-2.5 ng/mL. After the addition of SIR, the median dose required to keep TAC blood trough concentrations within the target range increased by 71.2% (range: 21.9-245.4%), dose-normalized TAC exposure (AUC) decreased to 67.1% and the dose-normalized C(max), a surrogate for absorption rate, to 53.8% (both geometric means) while terminal half-life (t1/2), a pharmacokinetic parameter characterizing systemic elimination, remained unchanged (p<0.93). Adding SIR to TAC-based immunosuppression in young pediatric renal transplant recipients results in a significant decrease of TAC exposure. TAC trough levels should be monitored frequently.