Department of Neurology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
Yonsei Med J. 2009 Aug 31;50(4):517-20. doi: 10.3349/ymj.2009.50.4.517. Epub 2009 Aug 19.
The pharmacokinetics of phenytoin is complicated by genetic and environmental differences. It is, therefore, important to monitor the serum concentrations in patients who receive phenytoin. Because most of the phenytoin in serum is bound to proteins, the level of serum albumin influences the amount of free phenytoin.
We compared the measured and calculated free phenytoin levels in epileptic patients who were taking phenytoin monotherapy, using the Sheiner-Tozer equation. A total of 49 patients (30 men and 19 women; age range, 15 - 87 years) were included in the study and their trough serum phenytoin and albumin concentrations were analyzed.
The linear correlation between free and total phenytoin concentrations was moderate (r = 0.822, p < 0.001). The mean difference between measured and calculated free phenytoin was large (0.65 +/- 0.88 microg/mL; 95% confidence interval (CI), -1.11 to 2.41). After dividing the patients into groups by albumin concentration, hypoalbuminemic patients (< 3.5 g/dL) more often had a greater percent difference (> or = 20%) than observed in the normoalbuminemic (> or = 3.5 g/dL) group.
In hypoalbuminemic patients, the measurement of free phenytoin level is necessary to properly evaluate the phenytoin level than that calculated from total phenytoin level.
苯妥英的药代动力学受遗传和环境差异的影响而变得复杂。因此，监测接受苯妥英治疗的患者的血清浓度非常重要。由于血清中的大部分苯妥英与蛋白质结合，因此血清白蛋白的水平会影响游离苯妥英的量。
我们使用 Sheiner-Tozer 方程比较了接受苯妥英单药治疗的癫痫患者的实测游离苯妥英水平和计算游离苯妥英水平。共有 49 名患者（30 名男性和 19 名女性；年龄范围 15-87 岁）纳入研究，并分析了他们的谷值血清苯妥英和白蛋白浓度。
游离和总苯妥英浓度之间存在中度线性相关（r = 0.822，p < 0.001）。实测游离苯妥英与计算游离苯妥英之间的平均差异较大（0.65 +/- 0.88 microg/mL；95%置信区间 [CI]，-1.11 至 2.41）。根据白蛋白浓度将患者分组后，低白蛋白血症患者（<3.5 g/dL）的百分比差异（>或=20%）大于正常白蛋白血症患者（>或=3.5 g/dL）组。
在低白蛋白血症患者中，与仅根据总苯妥英水平计算相比，测量游离苯妥英水平更有助于正确评估苯妥英水平。
