Clinical decision support of therapeutic drug monitoring of phenytoin: measured versus adjusted phenytoin plasma concentrations

BMC Medical Informatics and Decision Making

Research Article

Matthew D Krasowski¹  Louis E Penrod² 

[1] Department of Pathology, University of Iowa Hospitals and Clinics, 52242, Iowa City, IA, USA;Department of Physical Medicine and Rehabilitation, University of Pittsburgh, 15213, Pittsburgh, PA, USA;Baptist Health South Florida, 33176, Miami, FL, USA;

关键词: Therapeutic Drug Monitoring;    Electronic Health Record;    Computerize Physician Order Entry;    Computerize Physician Order Entry System;    Plasma Albumin Concentration;   

DOI  :  10.1186/1472-6947-12-7

 received in 2011-07-07, accepted in 2012-02-14,  发布年份 2012

来源: Springer

【 摘 要 】

BackgroundTherapeutic drug monitoring of phenytoin by measurement of plasma concentrations is often employed to optimize clinical efficacy while avoiding adverse effects. This is most commonly accomplished by measurement of total phenytoin plasma concentrations. However, total phenytoin levels can be misleading in patients with factors such as low plasma albumin that alter the free (unbound) concentrations of phenytoin. Direct measurement of free phenytoin concentrations in plasma is more costly and time-consuming than determination of total phenytoin concentrations. An alternative to direct measurement of free phenytoin concentrations is use of the Sheiner-Tozer equation to calculate an adjusted phenytoin that corrects for the plasma albumin concentration. Innovative medical informatics tools to identify patients who would benefit from adjusted phenytoin calculations or from laboratory measurement of free phenytoin are needed to improve safety and efficacy of phenytoin pharmacotherapy. The electronic medical record for an academic medical center was searched for the time period from August 1, 1996 to November 30, 2010 for patients who had total phenytoin and free phenytoin determined on the same blood draw, and also a plasma albumin measurement within 7 days of the phenytoin measurements. The measured free phenytoin plasma concentration was used as the gold standard.ResultsIn this study, the standard Sheiner-Tozer formula for calculating an estimated (adjusted) phenytoin level more frequently underestimates than overestimates the measured free phenytoin relative to the respective therapeutic ranges. Adjusted phenytoin concentrations provided superior classification of patients than total phenytoin measurements, particularly at low albumin concentrations. Albumin plasma concentrations up to 7 days prior to total phenytoin measurements can be used for adjusted phenytoin concentrations.ConclusionsThe results suggest that a measured free phenytoin should be obtained where possible to guide phenytoin dosing. If this is not feasible, then an adjusted phenytoin can supplement a total phenytoin concentration, particularly for patients with low plasma albumin.

【 授权许可】

CC BY   
© Krasowski and Penrod; BioMed Central Ltd. 2012