腎臟移植術後需長期使用免疫抑制劑預防移植腎臟之急性與慢性排斥反應，進而延長病人與移植腎臟之存活。Tacrolimus 藥理機轉是屬於calcineurin 抑制劑，為最常被使用之免疫抑制劑之一。研究發現，tacrolimus 血中濃度在個體內與個體間之變異性大與多重因素相關，又因其有效治療濃度區間狹窄且具有腎毒性，因此藥物療效與不良反應監測具有其重要性與急迫性。藥物在人體之總暴露量會直接影響藥物療效和不良反應，而抽血監測tacrolimus 波谷 (trough) 濃度為目前最廣為被使用的評估藥效方式。然而香港的學者研究指出，測單點tacrolimus 波谷濃度與其體內之暴露量相關性並不高(r = 0.34, p = 0.17)，建議使用藥物濃度—時間曲線下面積 (area under the concentration time curve, AUC) 的評估方法可以更精準監測tacrolimus 的藥效。其證實一個利用2 個時間點的血中濃度 ( 服藥後第2 小時與第4 小時 ) 所演算出的預估AUC0 ~ 12 迴歸公式，其判定係數r2 可達0.93。同時也建議移植術後6 週內之AUC 維持於210.0 ng•hr/mL ( 相當於波谷濃度12.5 ng/mL)，可有效評估病人體內的tacrolimus 暴露量是否足夠，並據以計算需調整之建議劑量。在此分享一腎臟移植案例，我們利用此一簡化的預估tacrolimus AUC0 ~ 12 公式來探討對病人最佳的使用劑量。

Long-term use of immunosuppressive agents post kidney transplantation can prevent graft kidney from acute and chronic rejection, and prolong patients and grafts survival. Tacrolimus (FK), a calcineurin inhibitor, was the most commonly used immunosuppressive agent. Due to a narrow therapeutic index and its large interpatient and intra-patient pharmacokinetic variability, therapeutic drug monitoring (TDM) is routinely implemented for individualization of the tacrolimus dose to maintain drug efficacy and minimize the adverse reaction, which is important and urgent. The total body exposure of drug (measured by the area under the concentration-time curve, AUC) may directly affect the efficacy and adverse effects of the drug, while the measurement of tacrolimus trough concentration is currently the most widely used for monitoring drug exposure. However, study has shown that tacrolimus trough concentration did not have a significant correlation with AUC0–12 (r = 0.34, p = 0.17), and recommended AUC may provide a more precise model for tacrolimus monitoring. They identify a two-time point regression equation using 2-hour (C2) and 4-hour (C4) tacrolimus concentrations, and the coefficient of determination r2 was improved to a level as high as 0.93. They also indicated that the AUC of 210.0 ng•hr/mL (equivalent to a trough concentration of 12.5 ng/mL) within 6 weeks post kidney transplantation, which is useful in estimating the overall drug exposure and hence facilitates easy adjustment to the optimal dose. Here we share a case of the kidney transplant recipient and use this abbreviated tacrolimus AUC0–12 regression equation to evaluate tacrolimus dosing.