Measurement of 10,11-dihydro-10-hydroxy-carbamazepine in serum and plasma by high-performance liquid chromatography

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Abstract
Oxcarbazepine is an antiepileptic drug (AED) used to treat partial seizures as a monotherapy or adjunctive therapy. Oxcarbazepine is metabolized in the liver to its active metabolite, 10,11-dihydro-10-hydroxy-carbamazepine (MHD). Optimal therapeutic effect and minimal toxicity can be achieved through monitoring MHD. Serum/plasma was mixed with internal standard (5-ethyl-5-p-tolylbarbituric acid) in methanol and centrifuged for 10 min. The mobile phase consisted of phosphate buffer and acetonitrile (466:168 v/v). The supernatant was analyzed by liquid chromatography (LC) with UV detection at 210 nm. The linearity ranged from 1.0 to 50.0 microg/mL with analytical recovery of 101.3%-110.8%. The limit of quantification was 1.0 microg/mL. The intra-assay coefficient of variation (CV) was 7.0% and 2.0% for serum samples spiked at 16.3 and 35.8 microg/mL, respectively. The inter-assay CV was 4.3% and 2.3% for serum controls at 7.2 and 23.8 microg/mL, respectively. The method was correlated with a commercial LC-mass spectrometry method using 41 leftover patient samples containing MHD at concentrations of 1.0-36.4 microg/mL, showing a slope of 1.09, an intercept of 1.2 and r=0.9520. No interference was observed from commonly administered AEDs. Commercial controls containing more than 100 therapeutic drugs and endogenous substances were also tested and showed no interference. This method is simple and effective for monitoring MHD in serum/plasma.

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