Simultaneous determination of felbamate and four metabolites in rat cerebrospinal fluid by high-performance liquid chromatography

Reactivity of atropaldehyde, a felbamate metabolite in human liver tissue in vitro

Antiepileptic therapy with a broad spectrum drug felbamate (FBM) has been limited due to reports of hepatotoxicity and aplastic anemia associated with its use. It was proposed that a bioactivation of FBM leading to formation of alpha,beta-unsaturated aldehyde, atropaldehyde (ATPAL) could be responsible for toxicities associated with the parent drug. Other members of this class of compounds, acrolein and 4-hydroxynonenal (HNE), are known for their reactivity and toxicity. It has been proposed that the bioactivation of FBM to ATPAL proceeds though a more stable cyclized product, 4-hydroxy-5-phenyltetrahydro-1,3-oxazin-2-one (CCMF) whose formation has been shown recently. Aldehyde dehydrogenase (ALDH) and glutathione transferase (GST) are detoxifying enzymes and targets for reactive aldehydes. This study examined effects of ATPAL and its precursor, CCMF on ALDH, GST and cell viability in liver, the target tissue for its metabolism and toxicity. A known toxin, HNE, which is also a substrate for ALDH and GST, was used for comparison. Interspecies difference in metabolism of FBM is well documented, therefore, human tissue was deemed most relevant and used for these studies. ATPAL inhibited ALDH and GST activities and led to a loss of hepatocyte viability. Several fold greater concentrations of CCMF were necessary to demonstrate a similar degree of ALDH inhibition or cytotoxicity as observed with ATPAL. This is consistent with CCMF requiring prior conversion to the more proximate toxin, ATPAL. GSH was shown to protect against ALDH inhibition by ATPAL. In this context, ALDH and GST are detoxifying pathways and their inhibition would lead to an accumulation of reactive species from FBM metabolism and/or metabolism of other endogenous or exogenous compounds and predisposing to or causing toxicity. Therefore, mechanisms of reactive aldehydes toxicity could include direct interaction with critical cellular macromolecules or indirect interference with cellular detoxification mechanisms.

Totally automated analysis by robotized PrepStation and liquid chromatography: direct-sample analysis of felbamate

A totally automated analysis of felbamate was developed by using a robotized PrepStation for extraction, followed by automated liquid chromatographic (LC) analysis and data reduction. This is one of the newer direct-sample analysis approaches by LC. Felbamate was a previously approved antiepileptic agent used to treat partial seizures with and without generalization and to treat Lennox-Gastaut syndrome in pediatric patients. However, due to the reported incidences of aplastic anemia, its clinical application was recently restricted to the treatment of the latter syndrome. The automated assay using Bench Supervisor, PrepStation, and LC, based on a previously developed manual method, used 200 microliters of serum standards, quality control, or patients' plasma. These were mixed with 600 microliters of internal standard (IS) W509 dissolved in acetonitrile for protein precipitation. After axial centrifugation and standing, aliquots of the clear supernatant were transferred and washed with hexane. Aliquots of the supernatant were transferred and injected into a high-performance liquid chromatograph (HPLC). HPLC parameters included an mu Bondapak C-18 column, phosphate/acetonitrile (8:2) as mobile phase, and detection at 214 nm. Retention times were 2.9 and 4.2 min for felbamate and IS, respectively. Calibration was linear for concentrations from 10 to 200 mg/L with r > 0.994. Precision studies showed coefficients of variation ranging from 2.7% to 8.8%. Correlation with the manual method showed that r = 0.934, slope = 1.048, intercept = -2.642, and n = 21. Phenobarbital coeluted with the IS. This study demonstrated the feasibility of using a robotized, automated method for monitoring felbamate, readily extended to monitoring other antiepileptic drugs with minimal modification.

Simultaneous determination of felbamate and three metabolites in rat and dog plasmas by high-performance liquid chromatography

An isocratic liquid chromatographic method employing one extraction step and a 150 mm x 4.6 mm I.D. Spherisorb ODS2, 3-microns HPLC column using UV-absorbance detection at 210 nm has been developed for the quantitation of felbamate and three felbamate metabolites in 0.100-ml aliquots of rat and dog plasmas. The linear quantitation range in rat plasma is 0.195-200 micrograms/ml for felbamate; 1.563-200 micrograms/ml for the p-hydroxy metabolite; 0.391-200 micrograms/ml for the 2-hydroxy metabolite; and 0.098-200 micrograms/ml for the monocarbamate metabolite. The linear quantitation range in dog plasma is 0.195-200 micrograms/ml for felbamate; 0.781-200 micrograms/ml for the p-hydroxy metabolite; 0.195-200 micrograms/ml for the 2-hydroxy metabolite; and 0.098-200 micrograms/ml for the monocarbamate metabolite.