Determination of chlorzoxazone and 6-hydroxychlorzoxazone in plasma by gas chromatography--mass spectrometry

Innovative localized surface plasmon resonance sensing technique for a green spectrofluorimetric assay of ketoprofen, paracetamol and chlorzoxazone in pharmaceutical preparations and biological fluids

A green, quick and sensitive spectrofluorimetric technique was investigated and validated for the assay of three different drugs namely, ketoprofen (KPN), paracetamol (PAR), and chlorzoxazone (CLX). The method is based on fluorescence quenching of the fluorescence probe, silver nanoparticles (SNPs). The fluorescence quenching of SNPs may be attributed to the complexation between each of the studied drugs with SNPs. The fluorescence of SNPs alone or after complexation with the studied drugs were measured at 485 nm (λ _ex 242 nm) without the need to extract the formed complex. Chemical reduction was employed for preparing SNPs, where silver nitrate was reduced by sodium borohydride in deionized water without adding organic stabilizer. SNPs were found soluble in water, had high stability and had a narrow emission band. The studied drugs were found to decrease the fluorescence of SNPs significantly through static quenching according to Stern-Volmer equation. Factors affecting the reaction between the drugs and NPs were carefully examined and optimized. Using the optimum conditions, the difference in the fluorescence intensity of SNPs before and after complexation with the studied drugs was in a good linear relationship with the concentration of the studied drugs, where (R ² = 0.9998, 0.9998 and 0.9991) in the ranges of 0.5-5.0, 0.15-3.0 and 0.5-9.0 μg mL^-1 for KPN, PAR and CLX, respectively. Validity of the proposed method was investigated according to ICH recommendations. The proposed technique was also employed for the analysis of each of the three drugs in commercial or laboratory prepared tablets and in spiked human plasma with very good recoveries as well as high level of accuracy and precision. This method was intended to the analysis of the proposed drugs in their single formulation and single drug administration. The suggested technique is considered an eco-friendly method, as it uses water as the safest and least expensive solvent. Moreover, the recommended technique does not involve solvent extraction of the formed complexes. Greenness assessment of the suggested procedure was accomplished by applying the four standard assessment tools. Consequently, the recommended method can be used in the routine quality control analysis of the cited drugs with minimum harmful effect on the environment as well as the individuals.

An LC-MS/MS Validated Method for Quantification of Chlorzoxazone in Human Plasma and Its Application to a Bioequivalence Study

A simple, sensitive, specific, accurate liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for determination of chlorzoxazone in human plasma was developed and validated to evaluate the pharmacokinetic characteristics of chlorzoxazone test or reference formulation. Sample preparation was achieved by one step protein precipitation and dilution with acetontrile. The chromatographic separation was performed at 40°C with a gradient mobile phase (0.3 mL/min) and a Shimadzu VP-ODS C18 analytical column (column size: 150 × 2.0 mm). TSQ quantum access triple-quadrapole MS/MS detection was operated in a negative mode by multiple reaction monitoring. Ion transitions at m/z 168.0→132.1 for chlorzoxazone and m/z 451.3→379.3 for repaglinide (internal standard) were used for the LC-MS/MS analysis. The calibration was linear (r ≥ 0.995) over the tested concentration range of 0.2-20 μg/mL for chlorzoxazone in plasma. Precision, accuracy, recovery, matrix effect and stability for chlorzoxazone were evaluated and were excellent within the range of tested concentrations. This method was successfully applied to a bioequivalence study in 20 healthy Chinese volunteers. This method could also contribute to the personalized medication and therapeutic drug monitoring of chlorzoxazone.

Inhibition of CYP2E1 by chlormethiazole as measured by chlorzoxazone pharmacokinetics in patients with alcoholism and in healthy volunteers

BACKGROUND

Chlormethiazole has been shown in in vitro studies, with use of rat and human liver microsomes, to specifically inhibit cytochrome P4502E1 (CYP2E1)-mediated activity by inhibition of the rate of CYP2E1 gene transcription. It is known that CYP2E1 is involved in the activation of many low-molecular-weight toxins and carcinogens and may be involved in the development of alcohol-induced liver disease.

METHODS

The pharmacokinetics of a single oral dose of 250 mg chlorzoxazone, a marker of the activity of CYP2E1, were measured in five healthy drug-free volunteers and in 16 patients with alcoholism receiving 1.2 gm or 2.4 gm chlormethiazole per day for 1, 2, or 3 days. The patients were starting an alcohol-withdrawal program and were supposed to have an induced CYP2E1 activity.

RESULTS

The results suggest that chlormethiazole strongly decreased chlorzoxazone clearance in the patients with alcoholism compared with clearance in the control subjects (3.98 +/- 1.8 L/hr versus 12.7 +/- 5.6 L/hr; p < 0.005), prolonged the elimination half-life (3.91 +/- 1.23 hours versus 1.12 +/- 0.34 hours; p < 0.001), and caused a threefold increase in the area under the concentration versus time curve of chlorzoxazone (73.0 +/- 35.5 mg.hr/L versus 21.3 +/- 13.7 mg.hr/L; p < 0.005). They also suggest that chlormethiazole significantly decreased the area under the concentration versus time curve of the metabolite 6-hydroxy-chlorzoxazone (4.56 +/- 1.27 mg.hr/L versus 7.1 +/- 1.84 mg.hr/L; p < 0.05).

CONCLUSION

Chlormethiazole administration seems to result in a marked reduction of CYP2E1 activity in subjects with high CYP2E1 activity and could at least partially explain the claimed hepatoprotective action of this drug.