Determination of clobazam, N-desmethylclobazam and their hydroxy metabolites in plasma and urine by high-performance liquid chromatography

Determination of Clobazam and Its Major Metabolite N-desmethylclobazam in Human Plasma with High-Performance Liquid Chromatography

Clobazam (CLB) is a benzodiazepine that is used in many types of epilepsy. Although therapeutic drug monitoring (TDM) of CLB is not routine, there is evidence that TDM may be of value in conditions where pharmacokinetic alterations are suspected. Therefore, determination of both CLB and its active metabolite concentrations is essential for TDM. Herein, we present a simple and practical method for determination of CLB and N-desmethylclobazam (NDMCLB) in human plasma by high-performance liquid chromatography (HPLC). The drugs were extracted by hexane:dichloromethane (1:1, v/v) from 0.3 mL plasma. The separation was carried out with a C18 reverse phase column using a mobile phase of water:acetonitrile (57:43, v/v) pumped at 0.8 mL/min. The analytes were detected at 228 nm. The method was linear over the concentration range 20–500 ng/mL for CLB and 200–3000 ng/mL for NDMCLB. The intra-day coefficient of variation (CV) was <10% for CLB and <6% for NDMCLB, while the inter-day CV for CLB was <16%. The metabolite inter-day CV was <6%. The accuracy of intra- and inter-day assessments determined for CLB and NDMCLB was within ±10%. This paper describes a rapid, reliable, and simple method for measuring CLB and its metabolite NDMCLB in human plasma. This UV-HPLC procedure offers acceptable precision and accuracy to quantify CLB and its metabolite in human plasma.

[Therapeutic drug monitoring of clobazam]

Clobazam is a 1,5 benzodiazepine available in France since 1975, used in add-on with the other anticonvulsant drugs in the treatment of refractory epilepsies of child and adult and for the treatment of anxiety of adult. It is mainly metabolized in desmethylclobazam, or norclobazam, active metabolite, present in a concentration approximately eight times superior to that of the parent drug, but with an activity of the order of 20 to 40% of that of clobazam. Elimination half-life of clobazam is of 18 h while that of norclobazam is from 40 to 50 h. There is a large interindividual variability in the plasma concentrations. Furthermore, clobazam being prescribed in add-on with the other anticonvulsant drugs in resistant epilepsies, concentration-effect relationship is difficult to bring to light, since, in many studies, the patients who did not answer received the highest doses. Adverse reactions are moderated, appearing more often for the highest concentrations; also the phenomenon of tolerance seems more frequent in high concentrations. However, because of the kinetic interactions, a dosage of clobazam and norclobazam can be useful in certain cases. There is no validated therapeutic range, but the usual concentrations are in the range of 100-300 microg/L for the parent drug and about ten times more for the metabolite. The level of proof of the interest of the Therapeutic Drug Monitoring for this molecule is estimated in: rather useless.

Simultaneous determination of clobazam and its major metabolite in human plasma by a rapid HPLC method

A rapid and specific HPLC method has been developed and validated for simultaneous determination of clobazam, the anticonvulsant agent, and its major metabolite in human plasma. The sample preparation was a liquid-liquid extraction with tuloene yielding almost near 100% recoveries of two compounds. Chromatographic separation was achieved with a Chromolith Performance RP-18e 100 mm x 4.6mm column, using a mixture of a phosphate buffer (pH 3.5; 10mM)-acetonitrile (70:30, v/v), in isocratic mode at 2 ml/min at a detection wave-length of 228 nm. The calibration curves were linear (r(2)>0.998) in the concentration range of 5-450 ng ml(-1). The lower limit of quantification was 5 ng ml(-1) for two compounds studied. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were in the range of 0.89-9.1% and 2.1-10.1% R.S.D., respectively. The developed procedure was applied to assess the pharmacokinetics of clobazam and its major metabolite following administration of a single 10mg oral dose of clobazam to healthy volunteers.

Effects of sufentanil or ketamine administered in target-controlled infusion on the cerebral hemodynamics of severely brain-injured patients*

OBJECTIVE

The manual injection of a bolus of opioid in patients with brain injury induces an increase in intracranial pressure related to a decrease in mean arterial pressure. Such an effect has not been observed with the use of ketamine. The use of target-controlled infusion would minimize or suppress this adverse effect of opioid. This study evaluated the effects of an increase in plasma concentrations of sufentanil or ketamine administered by target-controlled infusion on cerebral hemodynamics.

DESIGN

Prospective, randomized study.

SETTING

Intensive care unit in a trauma center.

PATIENTS

Thirty patients with severe traumatic brain injury.

INTERVENTIONS

Patients were assigned to receive sedation consisting of sufentanil-midazolam or ketamine-midazolam using target-controlled infusion. Twenty-four hours after the onset of sedation, the target concentrations of sufentanil or ketamine were doubled for 15 mins. Blood samples were collected to determine the actual plasma concentration of sufentanil and ketamine, before and 15 mins after concentration change.

MEASUREMENTS AND MAIN RESULTS

The baseline values of intracranial pressure and cerebral perfusion pressure were similar in both groups. The two-fold increase in drug concentrations did not involve a significant change for intracranial pressure, cerebral perfusion pressure, and mean velocity of middle cerebral artery in both the ketamine and the sufentanil groups. The measured plasma concentrations of sufentanil and ketamine were 0.4 +/- 0.2 ng/mL and 2.6 +/- 2.2 mug/mL, respectively, before the increase in concentrations and 0.7 +/- 0.4 ng/mL and 5.5 +/- 3.8 mug/mL after.

CONCLUSIONS

The present study shows that the increase in sufentanil or ketamine plasma concentrations using a target-controlled infusion is not associated with adverse effects on cerebral hemodynamics in patients with severe brain injury. The use of target-controlled infusion could be of interest in the management of severely brain-injured patients. However, there is a need for specific pharmacokinetic models designed for intensive care unit patients.

Analysis of certain tranquilizers in biological fluids

A review with 282 references is presented that deals with the reported methods of analysis of phenothiazines, thioxanthenes, and benzodiazepine derivatives of pharmaceutical interest. The review includes the methods adapted in biological fluids.

Simple and sensitive high-performance liquid chromatographic method for the determination of 1,5-benzodiazepine clobazam and its active metabolite N-desmethylclobazam in human serum and urine with application to 1,4-benzodiazepines analysis

A HPLC-UV determination of clobazam and N-desmethylclobazam in human serum and urine is presented. After simple liquid-liquid extraction with dichloromethane the compounds and an internal standard diazepam were separated on a Supelcosil LC-8-DB column at ambient temperature under isocratic conditions using the mobile phase: CH3CN-water-0.5 M KH2PO4-H3PO4 (440:540:20:0.4, v/v and 360:580:60:0.4, v/v for serum and urine, respectively). The detection was performed at 228 nm with limits of quantification of 2 ng/ml for serum and 1 ng/ml for urine. Relative standard deviations for intra- and inter-assay precision were found below 8% for both compounds for all the tested concentrations. The described procedure may be easily adapted for several 1,4-benzodiazepines.

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.

Monitoring of benzodiazepines (clobazam, diazepam and their main active metabolites) in human plasma by column-switching high-performance liquid chromatography

A column-switching high-performance liquid chromatographic method for the simultaneous determination of clobazam, diazepam and their main metabolites in human plasma is described. A 200-microliters plasma sample was directly injected into a precolumn filled with TSK-gel PW. After a washing step with potassium phosphate buffer, the retained substances were backflushed into a reversed-phase column with a mobile phase of acetonitrile-phosphate buffer-diethylamine. Various drugs frequently co-administered with clobazam or diazepam do not interfere with the determination.

Analysis of antiepileptic drugs

This review discussed various analytical methods for the determination of antiepileptic drugs and their metabolites in biological tissues. The emphasis was on the reports published since their last review [J. T. Burke and J. P. Thenot, J. Chromatogr., 340 (1985) 199]. Both chromatographic and immunological procedure were cited and compared. Methods for individual and simultaneous quantitation of standard antiepileptic drugs and their metabolites were considered. In addition, a discussion of free drug determination and procedures for new candidate antiepileptic drugs were included.

Chromatography of benzodiazepines

An overview of methods for the determination of benzodiazepines in biological media, based on the application of chromatographic techniques, is presented. A general discussion of the techniques in terms of stability, selectivity, validation, standardization, detection and sensitivity is given. No single technique can be claimed as the method of choice for benzodiazepines. Gas chromatography with electron-capture detection has some strong claims and shows generally good sensitivity and reproducibility. High-performance liquid chromatographic equipment is readily available in most laboratories. The ultimate choice of an assay method for benzodiazepines will be determined by the clinical application (routine monitoring, pharmacokinetics, overdose, forensic medicine) and by the characteristics of the benzodiazepine, the expertise of the analyst, the equipment available, the desired sensitivity and specificity and the time involved in method development or adaptation and validation.

Capillary gas chromatographic-mass spectrometric method for the identification and quantification of some benzodiazepines and their unconjugated metabolites in plasma

A gas chromatographic-mass spectrometric method for the identification and/or quantification of diazepam, clobazam, flunitrazepam, triazolam, midazolam, oxazepam and lorazepam and some of their desmethylated and hydroxylated metabolites in plasma is described. Benzodiazepines were extracted from plasma with butyl acetate at pH 9; the hydroxylated compounds were then silylated with N,O-bis (trimethylsilyltrifluoroacetamide). Analysis was performed using a compact mass-selective detector operating in the electron-impact mode. Depending on the concentration, identification was performed either by direct comparison of the observed mass spectra with reference spectra or by the relative intensities of the most intense and characteristic ions in the selected-ion monitoring (SIM) mode. Quantification was performed in the SIM mode using the most intense ion. The intra-assay precision and accuracy were better than 5-6%; linearity was satisfactory up to 1-2 micrograms/ml. The detection limit was 1-5 ng/ml for most of the benzodiazepines. This method can be easily used in clinical situations when a safe and rapid response is essential for patient treatment.

Screening procedure for benzodiazepines in biological fluids by high-performance liquid chromatography using a rapid-scanning multichannel detector

A sensitive and specific determination of benzodiazepines in biological fluids is described, based on reversed-phase high-performance liquid chromatography. The compounds are extracted with a C2 AASP cartridge within 5 min. The recovery ranges from 92 to 104% and is independent of the concentration. Using a suitable gradient elution, complete separation of nineteen benzodiazepines is achieved in 50 min with detection limits of less than 3 ng/ml in urine and 5 ng/ml in other biological fluids. Using a rapid-scanning multichannel detector, the identities of the benzodiazepines can be confirmed. Prazepam is employed as internal standard. The precision and accuracy of the described method are suitable for monitoring benzodiazepine levels in clinical studies and an example is given.

Determination of clobazam and its N-demethyl metabolite in serum of epileptic patients

We describe a gas-liquid chromatographic method, using a nitrogen-specific detector, which is suitable for the simultaneous quantitation of clobazam and its main metabolite N-demethyl clobazam in the serum of epileptic patients treated with other anticonvulsant co-medication. Flunitrazepam (internal standard) is added to the sample and after extraction with a toluene/ethyl acetate mixture (3 + 1 by vol), the organic extract is evaporated and the residue is reconstituted in a small volume of solvent and chromatographed on a 3% SP2250 column. The sensitivity limits are about 2 to 5 micrograms per liter of original sample.