Electromembrane extraction as a new approach for determination of free concentration of phenytoin in plasma using capillary electrophoresis

Abstract

Electromembrane extraction is a new membrane-based extraction method in which charged compounds are extracted by an electric field. So far, this method has been used to extract and isolate a variety of acidic and basic drugs from various samples, including blood and plasma. However, in this procedure, it is not yet clear whether only unbound fraction of a drug is extracted or the total drug. The aim of this study is to reveal the nature of drug extraction in the presence of plasma proteins. To determine the nature of the extraction, the electromembrane extraction was performed from plasma solutions of phenytoin with concentrations 0.03 and 1.0μg/mL, then the result was compared with the values obtained from the electromembrane extraction of ultrafiltrate of the same solutions (free concentration) and protein-free ultrafiltrate of plasma with final concentration of 0.03 and 1.0μg/mL (total concentration). For this purpose, EME followed by capillary electrophoresis coupled with diode array detection was optimized and validated. The results showed that the electromembrane extraction method was only able to extract the unbound fraction of phenytoin from plasma samples. The method was validated over a concentration range of 0.03-4μg/mL. The inter and intra-assay precisions were less than 6.7%. The phenytoin protein binding was also determined to be in agreement with the literature data and confirms the validity of this method. This sensitive and quick EME approach for determining the free concentration of a phenytoin, can be a good alternative to classic methods for therapeutic drug monitoring and pharmacokinetic studies.