A novel nanozyme doped ZnO/r-GO-based sensor for highly sensitive electrochemical determination of muscle-relaxant drug: cyclobenzaprine HCl.

A nanocomposite of Ce-doped ZnO/r-GO was synthesized using a conventional hydrothermal method. The synthesized nanocomposites were utilized for the purpose of sensitive and selective detection of cyclobenzaprine hydrochloride (CBP). The properties of the composite were extensively analyzed, including its morphology, structure, and electrochemical behavior. This study investigates the application of a modified glassy carbon electrode for the detection of CBP, a muscle relaxant used to treat musculoskeletal diseases that cause muscle spasms. The electrode is modified with Ce-doped ZnO/r-GO. Various detection methods, such as cyclic voltammetric and square wave techniques (SWV), were utilized. The composite material showed high effectiveness as an electron transfer mediator in the oxidation of CBP. The electrode showed a good response for SWV evaluations in CBP identification, with a minimum detection limit of 1.6 × 10-8 M and a wide linear range from 10 × 10-6 M to 0.6 × 10-7 M, under ideal conditions. The rate constant for charge transfer (ks) and the estimation of the electrochemical active surface area were obtained. A developed sensor exhibited desirable selectivity, long-lasting stability, and remarkable reproducibility. A sensor was used to analyze water, human serum, and urine samples, resulting in positive recovery results.

Pharmacokinetics of eperisone following oral administration in healthy Korean volunteers.

Eperisone is an oral muscle relaxant used to treat musculoskeletal diseases, which exhibits high pharmacokinetic (PK) variability in bioequivalence studies. The aim of this study was to characterize the PKs of eperisone following its oral administration to Korean volunteers through the conduct of a noncompartmental and population analysis. A total of 360 concentration-time measurements collected on two separate occasions from 15 healthy volunteers during a bioequivalent study of eperisone 50 mg (Murex® ) were used in the PK analysis. Noncompartmental analysis was performed using WinNonLinTM and population analysis was performed using NONMEM® . The possible influence of thirty demographic and pathophysiological characteristics on the PKs of eperisone were explored. Based on noncompartmental analysis mean eperisone elimination half-life, apparent clearance (CL/F), and apparent volume of distribution were estimated to be 3.81 h, 39.24 × 103  l/h × 103  L, respectively. During population PK modeling a two-compartment model with first-order absorption rate constant (typical population K a  = 1.5 h-1 ) and first-order elimination (typical population CL/F and apparent volume of distribution in the central compartment [V c /F] = 30.8 × 103  l/h and 86.2 × 103  l, respectively) best described the PKs of eperisone. Interindividual variability in CL/F and V c /F were estimated to be 87.9% and 130.3%, respectively and interoccasion variability in CL/F and V c /F were estimated to be 23.8% and 30.8%, respectively. Aspartate aminotransferase level and smoking status were identified as potential covariates that may influence the CL/F of eperisone. This is the first study to develop a disposition model for eperisone and investigate the potential influence of covariate factors on it PK variability.

Liquid chromatography high resolution mass spectrometry for the determination of baclofen and its metabolites in plasma: Application to therapeutic drug monitoring.

Baclofen is used to manage alcohol dependence. This study describes a simple method using liquid chromatography coupled to high-resolution mass spectrometry (LC-HR-MS) developed in plasma samples. This method was optimized to allow quantification of baclofen and determination of metabolic ratio of its metabolites, an oxidative deaminated metabolite of baclofen (M1) and its glucuronide form (M2). The LC-HR-MS method on Exactive® apparatus is a newly developed method with all the advantages of high resolution in full-scan mode for the quantification of baclofen and detection of its metabolites in plasma. The present assay provides a protein precipitation method starting with 100 µL plasma giving a wide polynomial dynamic range (R2 > 0.999) between 10 and 2000 ng/mL and a lower limit of quantitation of 3 ng/mL for baclofen. Intra- and inter-day precisions were <8.1% and accuracies were between 91.2 and 103.3% for baclofen. No matrix effect was observed. The assay was successfully applied to 36 patients following baclofen administration. Plasma concentrations of baclofen were determined between 12.2 and 1399.9 ng/mL and metabolic ratios were estimated between 0.4 and 81.8% for M1 metabolite and on the order of 0.3% for M2 in two samples.

Pharmacokinetics of methocarbamol and phenylbutazone in exercised Thoroughbred horses.

Methocarbamol (MCBL) is commonly used in performance horses for the treatment of skeletal muscle disorders. Current regulatory recommendations for show horses and racehorses are based on a single oral dose of 5 g, although doses in excess of this are often administered. The goal of the current study was to characterize the disposition of MCBL following higher dose administration and administration in combination with another commonly used drug in performance horses, phenylbutazone (PBZ). Exercised Thoroughbred horses were administered various doses of MCBL as a sole agent and MCBL in combination with PBZ. Blood samples were collected at various times, concentrations of MCBL and PBZ measured using LC-MS/MS and pharmacokinetic parameters calculated using compartmental analysis. Following administration of 15 g of MCBL, either as part of a single- or multiple-dose regimen, a number of horses exceeded the Association of Racing Commissioners International and the United States Equestrian Federation's recommended regulatory threshold at the recommended withdrawal time. There was not a significant difference between horses that received only MCBL and those that received MCBL and PBZ. Results of the current study support an extended withdrawal guideline when doses in excess of 5 g are administered.

Baclofen overdose treated with continuous venovenous hemofiltration.

PURPOSE: Overdose with baclofen, a derivative of the inhibitory neurotransmitter γ-aminobutyric acid, may lead to severe respiratory and central nervous system depression and can be life-threatening. Prolonged half-lives of baclofen, of up to 34 h, have been reported in patients after overdose. Hemodialysis has proven to be a successful approach to improve clearance of baclofen, but the value of continuous venovenous hemofiltration (CVVH) is unclear. We applied CVVH in a patient with acute baclofen overdose. METHODS: Pharmacokinetic measurements of baclofen in serum and hemofiltrate were made at six time points after hospital admission. Baclofen concentration-time data were analyzed using non-compartmental methods, and the relative contribution of clearance by hemofiltration to total baclofen clearance was calculated. RESULTS: Baclofen concentrations in serum varied between 1.81 and 0.05 mg/L. Concentrations of baclofen in hemofiltrate were within the same range (between 0.74 and 0.05 mg/L), and the elimination half-life during hemofiltration was estimated at 4.8 h. Total clearance and clearance via hemofiltration were estimated at 6.6 and 2.4 L/h, indicating that clearance could be increased by approximately 57 % by applying hemofiltration. CONCLUSIONS: The presented case demonstrates the usefulness of CVVH in the treatment of baclofen overdose and indicates that CVVH can be used as an alternative to hemodialysis in patients with overdose of baclofen.

[Lethal intoxication with baclofen].

The objective of the present study was to select and develop simpler methods for the quantitative determination of baclofen in blood with the use of HPLC and tandem MS (MS-MS) techniques and its qualitative determination in cadaveric organs by the GC/MS technique. These mathods were shown to be suitable for the purpose of forensic medical analysis, clinical, toxicological, and therapeutic monitoring. The special emphasis is laid on the methods used to investigate the biological materials obtained from the subjects who died from baclofen intoxication.

Population pharmacokinetics of oral baclofen in pediatric patients with cerebral palsy.

OBJECTIVE: To characterize the population pharmacokinetics (PK) of oral baclofen and assess impact of patient-specific covariates in children with cerebral palsy (CP) in order to support its clinical use. SUBJECTS DESIGN: Children (2-17 years of age) with CP received a dose of titrated oral baclofen from 2.5 mg 3 times a day to a maximum tolerated dose of up to 20 mg 4 times a day. PK sampling followed titration of 10-12 weeks. Serial R- and S-baclofen plasma concentrations were measured for up to 16 hours in 49 subjects. Population PK modeling was performed using NONMEM 7.1 (ICON PLC; Ellicott City, Maryland). RESULTS: R- and S-baclofen showed identical concentration-time profiles. Both baclofen enantiomers exhibited linear and dose/kg-proportional PK, and no sex differences were observed. Average baclofen terminal half-life was 4.5 hours. A 2-compartment PK model with linear elimination and transit absorption steps adequately described concentration-time profiles of both baclofen enantiomers. The mean population estimate of apparent clearance/F was 0.273 L/h/kg with 33.4% inter-individual variability (IIV), and the apparent volume of distribution (Vss/F) was 1.16 L/kg with 43.9% IIV. Delayed absorption was expressed by a mean transit time of 0.389 hours with 83.7% IIV. Body weight, a possible genetic factor, and age were determinants of apparent clearance in these children. CONCLUSION: The PK of oral baclofen exhibited dose-proportionality and were adequately described by a 2-compartment model. Our population PK findings suggest that baclofen dosage can be based on body weight (2 mg/kg per day) and the current baclofen dose escalation strategy is appropriate in the treatment of children with CP older than 2 years of age.

Serum concentration of eperisone hydrochloride correlates with QT interval.

BACKGROUND: Eperisone hydrochloride is a centrally acting muscle relaxant prescribed for muscle stiffness that acts by depressing the activities of α and γ efferent neurons in the spinal cord and supraspinal structures. Although a case of eperisone-induced severe QT prolongation had been reported, the relationship between serum eperisone concentration and QT interval remains obscure. OBJECTIVE: The aim of this study was to investigate the relationship between serum eperisone concentration and QT interval. METHODS: Four patients who overdosed on eperisone were admitted to our hospital between January 2010 and December 2011. We took simultaneous serial measurements of serum eperisone concentration and QT interval in the intensive care unit. In total, 22 measurement points were plotted for these patients. We analyzed the correlation between the serum eperisone concentration and corrected QT (QTc) interval. RESULTS: Three men and one woman (mean age, 50 years) overdosed on eperisone with an average dose of 3087.5 mg (therapeutic dose, 150 mg/day). The mean QTc interval at arrival was 592 ms (range, 444-825 ms), and the mean serum eperisone concentration at arrival was 1257.5 ng/mL (range, 14.5-4120.0 ng/mL). The correlation coefficient was 0.833 between serum eperisone concentration and QTc interval (P < .001). CONCLUSION: Serum eperisone concentration correlates with QTc interval in patients who overdose on eperisone.

Rapid simultaneous determination of eperisone, tolperisone, and tizanidine in human serum by using a MonoSpin® C18 extraction column and liquid chromatography/tandem mass spectrometry.

A method was developed for rapid toxicological analysis of eperisone, tolperisone, and tizanidine in human serum using a MonoSpin® C18 extraction column and LC/MS/MS. The method was validated for LOD, linearity, precision, and extraction recovery. This method was rapid with an LOD of 0.5 ng/mL, linearity range 1-500.0 ng/mL (r2 = 0.999), and RSD value below 14.6%. Extraction recovery from the sample was greater than 98.6, 98.8, and 88.5% for eperisone, tolperisone, and tizanidine, respectively. Results showed that combination of the MonoSpin C18 extraction column and LC/MS/MS is a simple and rapid method for the analysis of these three analytes, and a method is described for simultaneous quantitative determination of the analytes in human serum by LC/MSIMS. This method was used to determine the serum levels of eperisone in a patient with eperisone poisoning, and could be successfully applied for screening analyses in clinical cases other than poisoning.

The pharmacokinetics of methocarbamol and guaifenesin after single intravenous and multiple-dose oral administration of methocarbamol in the horse.

A simple LC/MSMS method has been developed and fully validated to determine concentrations and characterize the concentration vs. time course of methocarbamol (MCBL) and guaifenesin (GGE) in plasma after a single intravenous dose and multiple oral dose administrations of MCBL to conditioned Thoroughbred horses. The plasma concentration-time profiles for MCBL after a single intravenous dose of 15 mg/kg of MCBL were best described by a three-compartment model. Mean extrapolated peak (C0 ) plasma concentrations were 23.2 (± 5.93) µg/mL. Terminal half-life, volume of distribution at steady-state, mean residence time, and systemic clearance were characterized by a median (range) of 2.96 (2.46-4.71) h, 1.05 (0.943-1.21) L/kg, 1.98 (1.45-2.51) h, and 8.99 (6.68-10.8) mL/min/kg, respectively. Oral dose of MCBL was characterized by a median (range) terminal half-life, mean transit time, mean absorption time, and apparent oral clearance of 2.89 (2.21-4.88) h, 2.67 (1.80-2.87) h, 0.410 (0.350-0.770) h, and 16.5 (13.0-20) mL/min/kg. Bioavailability of orally administered MCBL was characterized by a median (range) of 54.4 (43.2-72.8)%. Guaifenesin plasma concentrations were below the limit of detection in all samples collected after the single intravenous dose of MCBL whereas they were detected for up to 24 h after the last dose of the multiple-dose oral regimen. This difference may be attributed to first-pass metabolism of MCBL to GGE after oral administration and may provide a means of differentiating the two routes of administration.

Pharmacokinetic evaluation of oral dantrolene in the dog.

The pharmacokinetics of dantrolene and its active metabolite, 5-hydroxydantrolene, after a single oral dose of either 5 or 10 mg/kg of dantrolene was determined. The effects of exposure to dantrolene and 5-hydroxydantrolene on activated whole-blood gene expression of the cytokines interleukin-2 (IL-2) and interferon-γ (IFN-γ) were also investigated. When dantrolene was administered at a 5 mg/kg dose, peak plasma concentration (Cmax ) was 0.43 µg/mL, terminal half-life (t1/2 ) was 1.26 h, and area under the time-concentration curve (AUC) was 3.87 µg·h/mL. For the 10 mg/kg dose, Cmax was 0.65 µg/mL, t1/2 was 1.21 h, and AUC was 5.94 µg·h/mL. For all calculated parameters, however, there were large standard deviations and wide ranges noted between and within individual dogs: t1/2 , for example, ranged from 0.43 to 6.93 h, Cmax ratios ranged from 1.05 to 3.39, and relative bioavailability (rF) values ranged from 0.02 to 1.56. While activated whole-blood expression of IL-2 and IFN-γ as measured by qRT-PCR was markedly suppressed following exposure to very high concentrations (30 and 50 µg/mL, respectively) of both dantrolene and 5-hydroxydantrolene, biologically and therapeutically relevant suppression of cytokine expression did not occur at the much lower drug concentrations achieved with oral dantrolene dosing.

Should postmortem subclavian blood be considered a peripheral or central sample?

The phenomenon of postmortem redistribution has long been described, but the processes driving it have not, as yet, been fully elucidated. Peripheral blood samples are currently used, when available, in an effort to minimize the effects of postmortem redistribution on drug concentrations, but what sources of blood are peripheral sources? A study was undertaken to determine if postmortem subclavian (SC) blood should be considered a peripheral or central blood sample. Twenty-eight cases were identified in which drugs were quantified in at least 2 of the following blood sources: femoral (F), SC, and heart (H); the concentrations found in each source were compared. Twenty different drugs were analyzed including 6 antidepressants, 6 opioid medications and metabolites, 3 benzodiazepines, 2 antihistamines, 2 sedative hypnotics, and 1 muscle relaxant. Analysis found that SC blood concentrations reflect neither F nor H blood concentrations, with the exception of the benzodiazepines where SC blood concentrations closely mirrored H blood concentrations. Overall, SC blood drug concentrations tended to be 1.3 times greater than F blood and 0.77 times less than H blood. Therefore, it is recommended that the exact source of the blood, rather than simply "peripheral" or "central," be notated on toxicology results to ensure appropriate interpretation.

CYP2C19 genetics in fatal carisoprodol intoxications.

INTRODUCTION: Carisoprodol, a frequently used muscle relaxant, can cause potentially fatal intoxications. Conversion to its active metabolite meprobamate is almost solely mediated by cytochrome P450 2C19 (CYP2C19), and mutations in this enzyme could have significant effects on serum concentrations. The objective of this study was to investigate the role of CYP2C19 genetics in mortalities due to carisoprodol intoxication. METHODS: The frequencies of CYP2C19 variant alleles were compared between the study group (n = 75) and two control groups, i.e. (1) deaths where carisoprodol was detected in the blood of the deceased, but intoxication was not the cause of death (control group A, n = 38), and (2) a healthy population not using carisoprodol (control group B, n = 185). In the study group and control A, the concentrations of carisoprodol and meprobamate were compared between the different genotype subgroups. RESULTS: The variant allele frequencies of CYP2C19 did not differ significantly between the study group and control groups. Moreover, no statistically significant difference in the concentrations of carisoprodol and meprobamate between the different genotype subgroups was found. CONCLUSIONS: This study finds no evidence for an important association between CYP2C19 genetics and mortality risk of carisoprodol. Other factors, such as co-administration with other drugs, likely play a more important role.

Baclofen intoxication: a "fun drug" causing deep coma and nonconvulsive status epilepticus--a case report and review of the literature.

UNLABELLED: The number of reports on baclofen intoxication has increased in recent years. We report a 15-year-old boy who was referred in a state of deep coma (Glasgow Coma Scale = 3). On clinical examination, he showed sinus bradycardia with normal blood pressure. On admission to the hospital, he presented intermittent short episodes of generalized tonic-clonic seizures. While results of imaging procedures and initial toxicological screening (including standard HPLC analysis and urine test) were negative, a nonconvulsive status epilepticus was diagnosed by electroencephalography (EEG). Identification of baclofen as causative agent was possible after the boy's father reported abusive baclofen intake. Subsequent toxicological target analysis of blood and urine samples confirmed the excessive intake of baclofen and showed a typical elimination pattern with a secondary release. Following 112 h of mechanical ventilation, the boy rapidly regained consciousness and recovered normal neurological behavior. CONCLUSIONS: The present case demonstrates the importance of considering baclofen overdosage in cases of severe coma in combination with an abnormal EEG pattern and sinus bradycardia with normal blood pressure levels, in particular as the substance is popular in internet reports promoting baclofen as a rather harmless "fun drug." Furthermore, it underlines the difficulty to identify baclofen as a causative agent without anamnestic information. Nevertheless, by reviewing existing literature on oral baclofen overdosage, it is possible to picture a nearly specific pattern of clinical symptoms in baclofen intoxication.

High-throughput and simultaneous analysis of eight central-acting muscle relaxants in human plasma by ultra-performance liquid chromatography-tandem mass spectrometry in the positive and negative ionization modes.

In this report, a high-throughput and sensitive method for analysis of eight central-acting muscle relaxants in human plasma by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in the positive and negative ionization modes using tolbutamide as internal standard is presented. After pretreatment of a plasma sample by solid-phase extraction with an Oasis HLB cartridge, muscle relaxants were analyzed by UPLC with Acquity UPLC BEH C(18) column and Acquity TQD tandem quadrupole mass spectrometer equipped with an electrospray ionization interface. The calibration curves for muscle relaxants spiked into human plasma equally showed good linearities in the nanogram per milliliter order range. The detection limits (signal-to-noise ratio = 3) was as low as 0.1-2 ng/mL. The method gave satisfactory recovery rates, accuracy, and precision for quality control samples spiked with muscle relaxants. To further validate the present method, 250 mg of chlorphenesin carbamate was orally administered to a healthy male volunteer, and the concentrations of chlorphenesin carbamate in plasma were measured 0.5, 1, 2, 4, 6, and 8 h after dosing; their concentrations in human plasma were between 0.62 and 2.44 µg/mL. To our knowledge, this is the first report describing simultaneous analysis of over more than two central-acting muscle relaxants by liquid chromatography-tandem mass spectrometry. This has been realized by the capability of our instrument for simultaneous multiple reaction monitoring of the target compounds in both positive and negative ionization modes. Therefore, the present method seems very useful in forensic and clinical toxicology and pharmacokinetic studies.

Vaginal diazepam use with urogenital pain/pelvic floor dysfunction: serum diazepam levels and efficacy data.

Vaginal diazepam is used off-label for pelvic floor dysfunction and urogenital pain, but serum levels with efficacy have not been reported until now. One clinician evaluated 21 women for overall, levator, and vulvar pain pre- and one-month post-daily diazepam treatment. One-month post-treatment assessments and serum diazepam levels were done; 62% were moderately or markedly improved. Levator examination pain scores were significantly improved, and vulvar pain scores decreased post-treatment. Serum diazepam levels were within normal limits. Vaginal diazepam may be helpful in treating pelvic floor/urogenital pain conditions.

A randomized single-dose, two-period crossover bioequivalence study of two fixed-dose Paracetamol/Orphenadrine combination preparations in healthy volunteers under fasted condition.

BACKGROUND: Paracetamol/Orphenadrine is a fixed dose combination containing 35 mg orphenadrine and 450 mg paracetamol. It has analgesic and muscle relaxant properties and is widely available as generics. This study is conducted to investigate the relative bioavailability and bioequivalence between one fixed dose paracetamol/orphenadrine combination test preparation and one fixed dose paracetamol/orphenadrine combination reference preparation in healthy volunteers under fasted condition for marketing authorization in Malaysia. METHOD: This is a single-center, single-dose, open-label, randomized, 2-treatment, 2-sequence and 2-period crossover study with a washout period of 7 days. Paracetamol/Orphenadrine tablets were administered after a 10-h fast. Blood samples for pharmacokinetic analysis were collected at scheduled time intervals prior to and up to 72 h after dosing. Blood samples were centrifuged, and separated plasma were kept frozen (- 15 °C to - 25 °C) until analysis. Plasma concentrations of orphenadrine and paracetamol were quantified using liquid-chromatography-tandem mass spectrometer using diphenhydramine as internal standard. The pharmacokinetic parameters AUC0-∞, AUC0-t and Cmax were determined using plasma concentration time profile for both preparations. Bioequivalence was assessed according to the ASEAN guideline acceptance criteria for bioequivalence which is the 90% confidence intervals of AUC0-∞, AUC0-t and Cmax ratio must be within the range of 80.00-125.00%. RESULTS: There were 28 healthy subjects enrolled, and 27 subjects completed this trial. There were no significant differences observed between the AUC0-∞, AUC0-t and Cmax of both test and reference preparations in fasted condition. The 90% confidence intervals for the ratio of AUC0-t (100.92-111.27%), AUC0-∞ (96.94-108.08%) and Cmax (100.11-112.50%) for orphenadrine (n = 25); and AUC0-t (94.29-101.83%), AUC0-∞ (94.77-101.68%) and Cmax (87.12-101.20%) for paracetamol (n = 27) for test preparation over reference preparation were all within acceptable bioequivalence range of 80.00-125.00%. CONCLUSION: The test preparation is bioequivalent to the reference preparation and can be used interchangeably. TRIAL REGISTRATION: NMRR- 17-1266-36,001; registered and approved on 12 September 2017.

Quantitative analysis of carisoprodol and meprobamate in whole blood using benzylcarbamate and deuterated meprobamate as internal standards.

Carisoprodol and meprobamate are frequently encountered drugs in impaired driving casework. Deuterated internal standards, although preferred, were not available until recently. Earlier published studies report the use of a variety of non-deuterated internal standards, many of which lack the chemical and physical similarities that are desired for quantitative analysis. Carisoprodol and meprobamate were determined in whole blood using solid-phase extraction and gas chromatography-mass spectrometry with benzylcarbamate and meprobamate-d(7) as internal standards. When benzylcarbamate was used as internal standard, the linear ranges for carisoprodol and meprobamate were 0-20 mg/L and 0-40 mg/L, respectively. The linear range increased to 100 mg/L when meprobamate-d(7) was used. Limits of detection for carisoprodol and meprobamate were 0.2 and 0.4 mg/L, respectively, regardless of the internal standard selection. The limit of quantitation for both drugs using either internal standard was 0.4 mg/L. Accuracies using benzylcarbamate and meprobamate-d(7) were 100-106% and 91-100%, respectively. Corresponding values for precision indicated intra-assay coefficients of variation of 2.6-4.3% for benzylcarbamate and 1.0-2.3% for meprobamate-d(7). No carryover was evident at 100 mg/L, the highest concentration tested, and no interferences were observed. Results indicated that either benzylcarbamate or meprobamate-d(7) is a suitable internal standard for quantitative determination of carisoprodol or meprobamate from whole blood.

Influence of diosmin pretreatment on the pharmacokinetics of chlorzoxazone in healthy male volunteers.

Chlorzoxazone, a centrally acting muscle relaxant, is a probe for cytochrome P450 2E1 (CYP2E1). The first part of the study consisted of oral administration of 250 mg of chlorzoxazone (Paraflex 250 tablet) alone to 12 healthy male volunteers. Blood samples were collected from the antecubital vein at intervals of 0, 0.5, 1, 2, 3, 4, 5, 6, 7, and 8 hours and urine voided during 0-4 and 4-8 hours was collected after the administration of chlorzoxazone. The second part of the study was conducted after a wash-out period of 7 days; 500 mg of diosmin (Venex 500) was administered daily for 9 days. On day 10, 250 mg of chlorzoxazone was administered. Blood and urine samples were obtained as mentioned above. Serum levels of chlorzoxazone were determined by HPLC. Pharmacokinetic parameters were determined based on non-compartmental model analysis using the computer program RAMKIN. Diosmin pretreatment significantly enhanced AUC, C(max) and t1/2 with a concomitant reduction in CL/f. The urinary excretion of 6-hydroxychlorzoxazone was decreased and unchanged chlorzoxazone was increased over 8 hours. Urinary metabolic ratios of 6-hydroxychlorazoxazone and chlorazoxazone were increased. After pretreatment with diosmin, overall excretion (0-8 h) of 6-hydroxychlorazoxazone and chlorazoxazone were decreased. Diosmin might have inhibited the microsomal CYP2E1-mediated hydroxylation of chlorazoxazone.