Predictive value of pretransplantation cyclosporine pharmacokinetic studies on initial post-transplantation dosing in pediatric kidney allograft recipients.

Despite the introduction of a variety of new immunosuppressive agents, cyclosporine A (CsA) has maintained a strong position in pediatric transplantation (Tx). Post-Tx dosing with CsA is a challenging task because of the narrow therapeutic window of the drug, the great individual variability of metabolism and the lack of consensus about the optimal dosage and targeted blood concentration. Sufficient administration of CsA may be protective against acute rejections and other early complications after Tx, which is crucial for the long-term survival of the graft. Individual doses based on pre-Tx pharmacokinetic studies might be helpful in achieving optimal early concentrations of CsA. To asses the usefulness of pharmacokinetic studies, we retrospectively compared the post-Tx doses administered with the individually predicted doses between 1988 and 1998. Multiple regression of data on 65 de novo renal transplant recipients, 1.1-15.5 yr old, was used to analyze the significance of the predicted dose, trough blood concentration of CsA (B-CsA), serum creatinine and age at the time of Tx in explaining the doses used during the first three post-Tx weeks. Patients were grouped according to age (<2, 2-8 and >8 yr), according to the predicted dose (within or outside +/-25% of age-group average), and according to the oral formulation of CsA. Standard dosing scheme was simulated by using age-specific average doses in the place of the individual predicted doses. Administered doses of CsA were high [averaging 22.6 (504), 20.7 (484), and 12.4 mg/kg/d (329 mg/m2/d) for patients <2, 2-8, and >8 yr old] but the average B-CsA remained in the target range of 250-450 microg/L. The predicted dose and age were significant parameters in explaining the administered doses during the first 3 wk after Tx. B-CsA and S-creatinine were non-significant. The predicted doses were used to initiate the dosing of CsA after Tx (R2 = 0.70) and adjustments to dosing were made during the next weeks (R2 = 0.59, 0.52). Multiple regression model showed better fit for 60% of our patients, who had atypical predicted doses (R2 = 0.74, 0.60, 0.64 for first, second and third post-Tx weeks, respectively), most remarkably in patients <2 yr of age, than for the study population as a whole. A simulated standard dose was not able to explain the administered doses of CsA. In conclusion, pre-Tx pharmacokinetic studies are valuable for determining individual post-Tx starting doses, especially for those patients who need high or low doses of CsA. Individual dosing led to relatively high initial CsA doses, which could be significant for the long-term survival of the graft.