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

Background: 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.

Methods: 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.

Results: 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.

Conclusions: This method is simple and effective for monitoring MHD in serum/plasma.