Determination of carbamazepine and its epoxide metabolite in plasma by high-speed liquid chromatography

A liquid-chromatographic method for the simultaneous determination of carbamazepine and its active metabolite (carbamazepine 10,11-epoxide) in plasma has been developed. The two compounds were identified in plasma by mass spectrometry. The lower limit of sensitivity is about 4 and 40 ng for the drug and its metabolite, respectively. 10,11-Dihydrocarbamazepine is used as internal standard for the determinations, which have precisions of 2.2 and 4.2%, respectively. No derivatization is needed. The specificity of the method for carbamazepine is shown by the significant correlation (r = 0.99) between the results obtained by this method and by mass fragmentography for the drug in plasma of patients.