A limited sampling strategy for the estimation of eight-hour neoral areas under the curve in renal transplantation

Neoral, the microemulsion formulation of cyclosporine (CsA), demonstrates more consistent bioavailability than the corn oil formulation Sandimmune. Because of Neoral's rapid peak and metabolism, 8-hour dosing has to be used in many pediatric and some adult patients to maintain adequate CsA peak-to-trough ratios. Although the area under the curve (AUC) is considered the best estimate of total drug exposure, it requires repeated blood sampling. Abbreviated AUC profiles yielding excellent estimates of Neoral AUC with twice daily dosing have been described, but no such abbreviated strategy exists for 8-hour dosing. One hundred fifty-two pharmacokinetic profiles in 23 patients were used to derive and prospectively test a limited two-sample strategy to predict Neoral AUCs in pediatric and adult patients on 8-hour dosing regimens of Neoral. The formula was derived from 69 full 8-hour CsA pharmacokinetic profiles in nine children who underwent renal transplantation. Stepwise forward linear and multiple-curve regression techniques assessed the relative importance of single and combination concentration time points to predict AUC. The abbreviated profiles were validated by comparing the mean prediction error for each regression equation. The abbreviated profile calculated by second (C2)- and fourth (C4)- hour levels (AUC = 129 + 1.84 x C2 + 4.39 x C4) correlated well with the full AUC (r² = 0.96; p < 0001). Mean prediction error was -0.4% ± 5.48%, and no values fell outside the clinically acceptable 15% prediction error limit. Prospectively applying the formula to 83 AUCs of 14 adults who underwent renal transplantation and were taking Neoral three times a day demonstrated an excellent fit (r² = 0.93; p < 0.001), with 94% of predicted values falling inside the ±15% limit. The authors describe the development of a clinically acceptable, limited sampling strategy to predict 8-hour Neoral AUCs in children and adults who underwent renal transplantation.