Estimation of the area under the curve for mycophenolic acid in adult renal transplant patients with concomitant tacrolimus using a limited sampling strategy

Objectives: The aim of this study was to develop a limited sampling strategy (LSS) for monitoring the use of mycophenolic acid (MPA) in maintenance therapy with tacrolimus (TCL) in renal transplant patients. Methods: Eighteen adult patients receiving a first transplant were investigated. All patients were treated with a combination of TCL, steroid and mycophenolate mofetil (MMF). Besides the predose trough concentration (C₀), whole blood samples were taken for measurement of the MPA concentration at 0·5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 h for a 14‐point 12‐h pharmacokinetic (PK) profile. Using stepwise linear regression analysis, an abbreviated area under the concentration time curve (AUC) was calculated using all 14, and any combination of sampling points to give an estimating equation with up to three predictors. Results: The equation derived from C₂, C₇ and C_12, for AUC estimation: AUC = (2·05 × C₂) + (8·51 ×C₇) + (2·29 × C₁₂) + 4·24. was found to be optimal. Using this formula, there was an excellent correlation between the estimated 3‐point AUC and AUC_{0–12 h}. To assess the agreement between the abbreviated methods and the full PK profile, we plotted the average AUC of the abbreviated estimates and the full PK profile. This Bland‐Altman analysis indicated good agreement to within ±2 SD and a prediction variability of 7·56 μg × h/mL. Conclusion: Our proposed three‐sampling‐point estimate of AUCs is clinically acceptable. However, the sampling times are inconvenient for outpatients, and is recommended only for monitoring MMF treatment of inpatients with suspected toxicity or at high risk of organ rejection.