Clinical Validation and Implications of Dried Blood Spot Sampling of Carbamazepine, Valproic Acid and Phenytoin in Patients with Epilepsy

To facilitate therapeutic monitoring of antiepileptic drugs (AEDs) by healthcare professionals for patients with epilepsy (PWE), we applied a GC-MS assay to measure three AEDs: carbamazepine (CBZ), phenytoin (PHT) and valproic acid (VPA) levels concurrently in one dried blood spot (DBS), and validated the DBS-measured levels to their plasma levels. 169 PWE on either mono- or polytherapy of CBZ, PHT or/and VPA were included. One DBS, containing ∼15 µL of blood, was acquired for the simultaneous measurement of the drug levels using GC-MS. Simple Deming regressions were performed to correlate the DBS levels with the plasma levels determined by the conventional immunoturbimetric assay in clinical practice. Statistical analyses of the results were done using MedCalc Version 12.6.1.0 and SPSS 21. DBS concentrations (Cdbs) were well-correlated to the plasma concentrations (Cplasma): r = 0.8381, 0.9305 and 0.8531 for CBZ, PHT and VPA respectively, The conversion formulas from Cdbs to plasma concentrations were [0.89×CdbsCBZ+1.00]µg/mL, [1.11×CdbsPHT−1.00]µg/mL and [0.92×CdbsVPA+12.48]µg/mL respectively. Inclusion of the red blood cells (RBC)/plasma partition ratio (K) and the individual hematocrit levels in the estimation of the theoretical Cplasma from Cdbs of PHT and VPA further improved the identity between the observed and the estimated theoretical Cplasma. Bland-Altman plots indicated that the theoretical and observed Cplasma of PHT and VPA agreed well, and >93.0% of concentrations was within 95% CI (±2SD); and similar agreement (1∶1) was also found between the observed Cdbs and Cplasma of CBZ. As the Cplasma of CBZ, PHT and VPA can be accurately estimated from their Cdbs, DBS can therefore be used for drug monitoring in PWE on any of these AEDs.

为便于医护人员为癫痫患者（patients with epilepsy, PWE）开展抗癫痫药物（antiepileptic drugs, AEDs）的治疗药物监测，本研究采用气相色谱-质谱联用（GC-MS）检测法，同时对一份干血斑（dried blood spot, DBS）中的三种抗癫痫药物——卡马西平（CBZ）、苯妥英（PHT）与丙戊酸（VPA）——的浓度进行同步测定，并验证干血斑检测浓度与血浆浓度的相关性。本研究纳入169例接受卡马西平、苯妥英或丙戊酸单药或联合用药的癫痫患者，采集一份含约15 µL血液的干血斑样本，通过气相色谱-质谱联用法同步完成药物浓度测定。采用简单戴明回归分析干血斑浓度与临床实践中常规免疫比浊测定法得到的血浆浓度之间的相关性。统计分析采用MedCalc Version 12.6.1.0与SPSS 21软件完成。干血斑浓度（Cdbs）与血浆浓度（Cplasma）具有良好相关性：卡马西平、苯妥英、丙戊酸的相关系数r分别为0.8381、0.9305与0.8531。由干血斑浓度推导血浆浓度的转换公式分别为：[0.89×CdbsCBZ+1.00]µg/mL、[1.11×CdbsPHT−1.00]µg/mL以及[0.92×CdbsVPA+12.48]µg/mL。在基于苯妥英与丙戊酸的干血斑浓度估算理论血浆浓度时，纳入红细胞（RBC）/血浆分配比（K）与个体血细胞比容水平，可进一步提升观测值与估算理论血浆浓度之间的一致性。布兰德-奥特曼图（Bland-Altman plots）结果显示，苯妥英与丙戊酸的理论血浆浓度与观测血浆浓度一致性良好，超过93.0%的浓度值处于95%置信区间（±2SD）内；卡马西平的观测干血斑浓度与血浆浓度也呈现出相似的1:1一致性。由于卡马西平、苯妥英与丙戊酸的血浆浓度可通过其干血斑浓度准确估算，因此干血斑可用于接受上述任意一种抗癫痫药物治疗的癫痫患者的治疗药物监测。