Analysis of antiepileptic drugs

Therapeutic drug monitoring of lamotrigine using capillary electrophoresis. Evaluation of assay performance and quality assurance over a 4-year period in the routine arena

The performance of a capillary zone electrophoresis (CZE)-based assay for lamotrigine (LAMO) in human plasma and serum with complete internal and external quality assurance over an extended period of time is reported. The assay, originally reported by Shihabi and Oles [J. Chromatogr. B 683 (1996) 119], is based upon protein precipitation by acetonitrile and analysis of an aliquot of the acidified supernatant and was adopted in our laboratory for routine use with multi-level internal calibration on different commercial instruments. Evaluation of the calibration and control data of 103 sets of analysis and data from four years of external quality assurance based upon analysis of four-monthly sera containing LAMO and eight other anticonvulsants in sub-therapeutic, therapeutic or toxicological concentration levels revealed the robustness of the CZE-based assay and its suitability for therapeutic drug monitoring of LAMO in a routine setting. CZE data obtained in single determinations were found to compare well with the spike values and the mean of HPLC data determined in 50-70 laboratories. Furthermore, the gathered data were evaluated retrospectively using single-level internal calibration. When applied with caution, this approach was determined to produce slightly higher but otherwise equivalent drug concentrations. For the 4 years of routine operation with external quality control, the reported laboratory ranking was between 19 (out of 67 participating laboratories) and 43 (69). This is the first account of a CZE-based drug assay with complete external quality assessment.

Separation of benzodiazepines on a new carbohydrate-based chiral stationary phase for HPLC

Several benzodiazepines were enantioresolved on a new carbohydrate chiral stationary phase based on maltooligosaccharides. The role of organic modifier, ionic strength, pH and temperature are examined and the results are discussed. In general, selectivity and retention were found to decrease with increasing organic modifier concentration. The appearance of two peaks for diazepam suggests that the reported separations are based on separation of conformers and was supported using circular dichroism detection. Counterintuitively, resolution and enantioselectivity were found to improve with increasing temperatures.

Analysis of clobazam and its active metabolite norclobazam in plasma and serum using HPLC/DAD

This report describes a simple reversed-phase high-performance liquid chromatographic (HPLC) method with automated solid-phase extraction (SPE) for analysing clobazam and norclobazam concentrations in human serum or plasma. For the HPLC analysis the samples and standards are prepared with an ASPEC automatic sample preparer using 100-mg Bond-Elut C-18 solid-phase extraction columns. The HPLC method is an isocratic method with a mobile phase of acetonitrile:methanol:10 mmol l-1 dipotassium hydrogen phosphate, pH 3.7 (30:2:100), at a flow rate of 1.5 ml min-1. The benzodiazepines are detected with a diode array detector (DAD) at 240 nm and the peak purity analyses are performed at 210-365 nm. The recovery is over 97% for both analytes, and it is independent of the drug concentration. The intra-assay CVs vary between 0.7 and 2.2% and inter-assay CVs between 3.8 and 4.6% at therapeutic drug concentrations. The detection limit is 15 nmol l-1. The assay is linear from 30 to 20,000 nmol l-1 (clobazam) and from 170 to 105,000 nmol l-1 (norclobazam). This method leads to a very good separation of norclobazam from carbamazepine and phenytoin. None of the anti-epileptic or antidepressant drugs tested interfere with the assay.

Simultaneous determination of antiepileptic drugs and their metabolites, including chiral compounds, via beta-cyclodextrin inclusion complexes by a column-switching chromatographic technique

Using beta-cyclodextrin as a mobile-phase additive, a column-switching chromatographic system equipped with two 25-mm short ODS cartridge columns and two UV detectors was successfully employed for the simultaneous determination of some antiepileptic drugs and their metabolites, including chiral compounds, in human serum. The compounds examined were phenobarbital, zonisamide, phenytoin and its metabolites, S- and R-5-(p-hydroxyphenyl)-5-phenylhydantoin, R- and S-mephobarbital, carbamazepine and its main metabolites, 10,11-dihydro-10-11-epoxycarbamazepine and trans-10,11-dihydroxy-10,11-dihydrocarbamazepine (as a racemate), and allobarbital (as an internal standard).

Systematic toxicological analysis of drugs and their metabolites by gas chromatography-mass spectrometry

Gas chromatographic-mass spectrometric (GC-MS) procedures for the systematic toxicological analysis of several categories of drugs relevant to clinical toxicology, forensic toxicology and doping control are reviewed. Papers from 1981 to 1991 are taken into consideration. They describe the detection of acute or chronic intoxication and the detection of drug abuse. Screening procedures are included for the following categories: barbiturates and other sedative-hypnotics, anticonvulsants, benzodiazepines, antidepressants, phenothiazine and butyrophenone neuroleptics, central stimulants (amphetamines, cocaine), hallucinogens (LSD, phencyclidine, tetrahydrocannabinol), opioid (narcotic) and other potent analgesics, non-opioid analgesics, antihistamines (histamine H1-receptor blockers), antiparkinsonian drugs, beta-blockers (beta-adrenoceptor blockers), antiarrhythmics (class I and IV), diuretics, laxatives and their metabolites. Methods for confirmation of results obtained by screening procedures using immunoassay or chromatographic techniques are also included. GC-MS procedures for the simultaneous detection of several categories of drugs, the so-called "general unknown analysis", are reviewed. The toxicological question to be answered and the consequence for the choice of an adequate method, the sample preparation and the chromatography itself are discussed. The basic information about the biosample assayed, work-up, GC column, mass spectral detection mode, reference data and sensitivity of each procedure are summarized in tables, arranged according to the category of drug. Examples of typical GC-MS applications are presented. Fragment ions that are suitable for mass spectral screening for particular categories of drugs and for general unknown are tabulated.

Analysis of antiepileptic drugs in human plasma using micellar electrokinetic capillary chromatography

We describe a method for the simultaneous determination of antiepileptic drugs (ethosuccimide, phenytoin, primidone, phenobarbital, carbamazepine and valproic acid) by micellar electrokinetic capillary chromatography using sodium dodecyl sulphate as the micellar phase. Factors affecting the micellar electrokinetic separation were studied for the quantitative determination of these drugs in human plasma. The confirmation of the peaks and the specificity of the method were investigated by combining multiwavelength detection with micellar electrokinetic capillary chromatography.