Simultaneous determination of five anti-epilepsy drugs in human plasma using liquid chromatography-mass spectrometry

A new liquid chromatography-mass spectrometry method for the determination of carbamazepine, clonazepam, alprazolam, estazolam and phenytoin in human plasma has been developed by using diazepam as an internal standard. Chromatographic separation was performed on a Zorbax SB-C18 column (30 mm x 2.1 mm, 3.5 mu m) with a mobile phase consisting of methanol and aqueous 25 mM ammonium acetate using gradient elution. A diethyl ether extraction method was used for the extraction of five anti-epilepsy drugs. The final extract was injected for analysis by LC-MS/MS. The method was validated within the concentration range of 50-5000 ng mL(-1) for five anti-epilepsy drugs. The precision of the assay (RSD%) was less than 10% at all concentration levels within the tested range. The method recoveries for all samples were more than 90%. The results indicate that the method is specific, sensitive and accurate, and suitable to study the pharmacokinetics, to adjust the dosage for individual administration, and to monitor the drug-concentration and drug abuse of the five anti-epilepsy drugs.