Metaxalone (Skelaxin(R))-Related Death

The case history and toxicological findings of a fatal multi-drug overdose involving metaxalone (Skelaxin) are presented. Gas-liquid chromatography with flame-ionization detection and gas chromatography-mass spectrometry were used to determine the following drug concentrations (mg/L) in aortic blood: 19 mg/L metaxalone; 190 mg/L acetaminophen; 0.28 mg/L hydrocodone; and < 0.1 mg/L diazepam, nordiazepam, amitriptyline, and nortriptyline. The following concentrations of metaxalone were reported in alternate specimens: 17 mg/L in femoral blood; 44 mg/L in bile; 70 mg/kg in liver; 7 mg/L in urine; 202 mg/kg in gastric contents; and 14 mg/L in vitreous humor. These concentrations were determined using both direct extraction and the method of standard addition. The quantitative results obtained by both procedures were in good agreement. Because of the limited information published on metaxalone toxicity, the pathologist assigned the manner and cause of death as accidental acute hydrocodone intoxication. Four additional cases in which metaxalone was present were analyzed for comparison. Two cases were probable drug-related deaths and had metaxalone aorta blood concentrations of 18 and 11 mg/L. The other two cases had therapeutic metaxalone concentrations in the aortic blood of < 0.75 and 2.1 mg/L.

Simple method for the assay of eperezolid in Brain Heart Infusion broth by high-performance liquid chromatography

A sensitive high-performance liquid chromatography (HPLC) method was developed and validated for quantification of eperezolid in Brain Heart Infusion (BHI) broth. Linezolid was employed as internal standard and sample deproteinization with methanol was used. Calibration standards ranged from 0.10 to 20 mg/l. Recovery was approximately 100% at the concentrations examined. Eperezolid was stable in the autosampler vial for at least 72 h at ambient temperature and in BHI broth for 72 h at 37 degrees C. The intra- and inter-day accuracy and reproducibility (relative standard deviation, R.S.D.) were less than 12.3%. This assay is rapid and ideal for analysis of a large number of samples.

Peritoneal dialysis fluid concentrations of linezolid in the treatment of vancomycin-resistant Enterococcus faecium peritonitis

OBJECTIVE

To determine linezolid concentrations in peritoneal dialysis fluid after multiple oral doses of the drug in a 46-year-old man with vancomycin-resistant Enterococcus faecium peritonitis who was undergoing peritoneal dialysis.

METHODS

After administration of oral linezolid 600 mg twice/day was started, peritoneal dialysis fluid was collected at the end of several 4- and 8-hour dwell times and submitted for analysis of linezolid concentration. Before linezolid therapy was begun, and immediately after several peritoneal dialysis exchanges, 30 ml of expended peritoneal dialysis fluid was collected in a sterile container and immediately frozen at -70 degrees C until analysis by high-performance liquid chromatography.

RESULTS

Peritoneal dialysis concentrations of linezolid greater than 4 microg/ml were achieved after the first dose of linezolid and maintained after repeated doses. During the course of therapy, mean linezolid concentrations in peritoneal dialysis fluid tended to increase (mean 7.60 pg/ml, range 3.54-16.2 microg/ml). All assayed peritoneal dialysis samples demonstrated linezolid concentrations greater than 4 microg/ml at the end of 4- or 8-hour dwell times, except for one level after a missed dose on linezolid treatment day 3. Duration of dwell times did not appear to correlate with linezolid concentrations.

CONCLUSION

In this patient, linezolid 600 mg twice/day penetrated into peritoneal dialysis fluid at or above the concentrations necessary to treat common gram-positive bacteria. Linezolid therapy is likely to have a role in peritoneal dialysis-associated peritonitis based on its antimicrobial activity, pharmacokinetic properties, ease of administration, and tolerability.

Simple method for the assay of linezolid in Brain Heart Infusion broth by high-performance liquid chromatography

A simple HPLC method was developed and validated for quantification of linezolid in Brain Heart Infusion (BHI) broth. Eperezolid was employed as internal standard and the sample pre-treatment procedure was simple. Calibration standards ranged from 0.05 to 16 mg/L. Accuracy was within 7.8% and reproducibility (RSD) was less than 8.3%. Recovery was approximately 100% at all concentrations examined. Linezolid was stable in the autosampler insert for at least 24 h at ambient temperature and in BHI for 72 h at 37 degrees C. This assay is rapid and ideal for analysis of a large number of samples.

[HPLC determination of zolmitriptan and its related substances]

OBJECTIVE

To develop an analytical method and quality control for determination of zolmitriptan and related substances.

METHODS

Zolmitriptan and related substances were separated and determined on a shimadzu CLC-C(8) column (150 mm x 6 mm, 10 microm) with a mobile phase of acetonitrile-10 mmol/L phosphate buffer (25:75 pH 7.5) and a flow-rate of 1 ml/min; the UV-VIS detector was operated at 229 nm.

RESULT

The limit of detection for the related substances was 0.5 ng on the zolmitriptan basis (S/N >3). Linear calibration curve was gene rated from 4 - 40 microg/ml with a correlation coefficient of 0.9999. The recovery rate of zolmitriptan was 99.1% with a standard deviation of 0.2%. The results of HPLC method were consistent with those of nonaqueous titration method.

CONCLUSION

HPLC method is a rapid sensitive and accurate method for the determination of zolmitriptan and its related substances.

Clomazone dissipation, adsorption and translocation in four paddy topsoils

Laboratory experiments about the dissipation, adsorption and translocation in four paddy topsoils were conducted in this paper. From the results it can be concluded as follows: the dissipation rate of clomazone differed greatly in different paddy soil derived from different parent materials. The half-lives for clomazone degradation in paddy soils ranged from 5.7 to 22.0 d. The order of clomazone dissipation rate was reddish yellow paddy soil > alluvial sandy paddy soil > yellow clayey paddy soil > purple sandy paddy soil. Clomazone sorption quantity was significantly correlated with organic carbon (R2 = 0.62) and clay content(R2 = 0.67) in the tested paddy soils. Positive correlation was found between apparent Kd value and cation exchange content(CEC). The consequences for the adsorption of different soils were purple sandy paddy soil > yellow clayey paddy soil > reddish yellow paddy soil > alluvial sandy paddy soil. Under the simulated rainfall of 200 mm through four different unsaturated soil lysimeters over 24 h, clomazone was readily to be leached into lower surface soil and there was about 2.6%--4.2% of applied clomazone leached out of 20 cm cultivated soil layer. Translocation experiments showed that the order of clomazone leaching ability was: alluvial sandy paddy soil > reddish yellow paddy soil > yellow clayey paddy soil > purple sandy paddy soil. Simple regression results manifested that factors like CEC, organic carbon, clay, and adsorption rate constant had been negatively correlated with the percentage of clomazone loss from soil lysimeters.

Development of a liquid chromatography method for the determination of linezolid and its application to in vitro and human microdialysis samples

Linezolid is a new, promising antibacterial agent to treat severe infections. A rapid HPLC assay using UV detection for the determination in microdialysate and human plasma was developed. After sample preparation, using acetonitrile for plasma and water for microdialysate, 20 microl was injected and separated on a RP-18 column. Overall, the assay exhibited good precision and accuracy. The diffusion properties of linezolid investigated in in vitro microdialysis experiments revealed a mean relative recovery of 77.5% (CV: 5.4%; delivery and recovery experiments). Following characterization of linezolid in in vitro microdialysis, the setting is suitable for application in clinical studies.

High-performance liquid chromatographic analysis of DA-7867, a new oxazolidinone, in human plasma and urine and in rat tissue homogenates

An HPLC method was developed for the determination of a new oxazolidinone, DA-7867 (I), in human plasma and urine and in rat tissue homogenates. To 100 microl of biological sample, 300 microl acetonitrile and 50 microl methanol containing 10 microg/ml DA-7858 (the internal standard) were added. After vortex-mixing and centrifugation, the supernatant was evaporated under a gentle stream of nitrogen. The residue was reconstituted in 100 microl of the mobile phase and a 50-microl aliquot was injected directly onto the reversed-phase (C(18)) column. The mobile phase, 20 mM KH2PO4:acetonitrile (75:25, v/v) was run at a flow rate of 1.5 ml/min and the column effluent was monitored by a UV detector set at 300 nm. The retention times of I and DA-7858 were approximately 6.5 and 8.7 min, respectively. The detection limits of I in human plasma and urine and in rat tissue homogenates were 20, 20, and 50 ng/ml, respectively.

Polydrug fatality involving metaxalone

A 29-year old female with a history of depression was found dead in a hotel room. The death scene investigation found empty pill bottles and an empty liter bottle of wine. Metaxalone, a centrally acting muscle relaxant, along with citalopram, ethanol, and chlorpheniramine were identified in the postmortem samples and quantitated by gas chromatography-mass spectrometry. The concentration of metaxalone in femoral vein blood was 39 mg/L. The heart blood concentration was 54 mg/L. Femoral vein blood concentrations of citalopram and chlorpheniramine were 0.77 mg/L and 0.04 mg/L, respectively. Ethanol levels were 0.13 g/dL in vitreous and 0.08 g/dL in heart blood. Other tissue samples were also analyzed. The authors consider the metaxalone concentrations toxic and potentially fatal. The citalopram concentrations were lower than those reported in fatal cases for this drug alone. Death was ascribed to polydrug abuse/overdose with metaxalone a major contributor. This represents the first reported case to our knowledge in which a metaxalone overdose significantly contributed to death.

Identification of a furazolidone metabolite responsible for the inhibition of amino oxidases

1 Furazolidone, a drug widely used in human and veterinary medicine, exhibits inhibition of monoamine oxidase activity, as observed in the tissues of a number of different animal species, including man. The aim of the current study was to determine which of the two possible metabolites, 3-amino-2-oxazolidone (AOZ) or beta-hydroxyethylhydrazine (HEH), a well-known carcinogenic compound, is involved in the toxicological effects reported. 2 A new spectrometric method was set up to differentiate intracellular HEH from AOZ inside cells. This method works well at low pH where both AOZ and HEH are free in solution and available to react with the chemical chromophore (DAB). 3 The results confirm that furazolidone has to be metabolized in the intact cell in order to exhibit mitochondrial monoamine oxidase inhibition, whereas AOZ itself is able to exert a reversible monoamine oxidase inhibition. AOZ also inhibits bovine serum amino oxidase. On the contrary, HEH gives irreversible inhibition of both enzymes. However, the reversible nature of the AOZ inhibition with respect to HEH suggests that the two metabolites act by different mechanisms which do not require the biotransformation of AOZ to HEH. 4 Cell lysates, previously incubated with AOZ, were directly analysed and the formation of HEH from AOZ was not detected, supporting the conclusion that the amino oxidase inhibition observed on treatment with furazolidone was attributable to AOZ and not to HEH.

Plant-derived biomolecules in fermented cabbage

The formation of plant-derived biomolecules during sauerkraut fermentation was studied. Cabbage was fermented with a starter culture, and the results were compared to the results of spontaneous fermentation. The concentration of flavonoids and glucosinolates was analyzed by HPLC, and that of the glucosinolate breakdown products, by GC-MS. Of the 20 different flavonoids tested, only kaempferol was found (0.9 mg/ kg FW, fresh weight). The content of kaempferol remained constant in the cabbage fiber matrix over the fermentation process. The nitrite concentration was below the detection limit in both fermentations. The total glucosinolate content in the raw material was 3.71 micro mol/g DW, dry weight. Glucosinolates were totally decomposed in both fermentations during two weeks, and different types of breakdown products were formed. Isothiocyanates, indole-3-carbinol, goitrin, allyl cyanide, and nitriles were determined in the fermented cabbage. Isothiocyanates and allyl cyanide were the predominant breakdown products in both fermentations. Sulforaphane nitrile and goitrin were found only in small quantities in the end products.

Resolution of ternary mixtures of nitrofurantoin, furaltadone and furazolidone by partial least-square analysis to the spectrophotometric signals after photo-decomposition

An UV spectroscopic method is proposed to analyze mixtures of the nitrofuran derivatives, nitrofurantoin, furaltadone and furazolidone, used in veterinary. The change of absorption spectra due to photo-decomposition is used. A 20% dimethylformamide/water, basic medium of pH 9.4 (ammonium chloride/ammonia) and a time of irradiation of 15 s are selected. Calibration graphs are established, with the percentage of decrease of absorbance as analytical signal, in the range 2-10 microg ml(-1). To analyze mixtures of the three compounds the partial least-squares (PLS) multivariate analysis method is used with the spectra obtained by subtracting the spectra after irradiation to the original spectra. Good results have been obtained in the analysis of synthetic samples and a formulation containing all these compounds.

AAS and AES determination of furaltadone, methadone and trazodone in pharmaceutical formulations

Ion-associate complexes of furaltadone, methadone and trazodone hydrochlorides with [Cd(SCN)(4)](2-) and [Zn(SCN)(4)](2-) were precipitated and the excess unreacted cadmium or zinc complex was determined. A new method using atomic emission and atomic absorption spectrometry for the determination of the above drugs in pure solutions and in pharmaceutical preparations is given. The drugs can be determined by the affort method in the ranges 7.2-72.16, 6.9-69.18 and 8.1-81.6 microg/ml solutions of the three drugs, respectively.

Evaluation of the residues of furazolidone and its metabolite, 3-amino-2-oxazolidinone (AOZ), in eggs

The use of furazolidone in food-producing animals is banned within the EU. Detection of the protein-bound side-chain metabolite, 3-amino-2-oxazolidinone (AOZ), in animal tissues is the most effective method of enforcing the ban. The study was undertaken to find out if the same applies to eggs. The concentrations of furazolidone and AOZ in eggs reached a plateau of approximately 360-380 microg kg(-1) by the fourth day of treating birds with 400 mg kg(-1) furazolidone. After a 4-day withdrawal from treatment, intact furazolidone could not be detected. AOZ residues could still be detected up to 21 days following withdrawal from treatment. During treatment, most intact furazolidone residues occur in the albumen. For AOZ, there is a more even distribution of residues between albumen and the yolk. The concentration of furazolidone in egg homogenates stored at -20 degrees C decreases by 44% after 55 days. AOZ residues are stable during this period. From these results, it is clear that AOZ is a more suitable marker residue than the parent compound for monitoring concentrations of the drug in eggs.

Determination of linezolid in human serum and urine by high-performance liquid chromatography

An HPLC method is described for the determination of the new oxazolidinone antibiotic linezolid (I) in human biofluids. After precipitation of serum proteins with perchloric acid the protein free supernatant was separated by isocratic reversed-phase chromatography on a Nucleosil-100 5C18 column. The mobile phase consisted of a mixture of acetonitrile: sodium acetate buffer: water (180:100:720, v/v) adjusted to pH 3.7. Urine was diluted with aqueous buffer solution. The column eluate was monitored at 250 nm. Validation of the method yielded satisfactory results for serum (and urine); detection limit 0.07 mg/l (2.4), lower limit of quantitation 0.14 mg/l (4.7), linear range 20 mg/l (500), imprecision within series (c.v.) 1.8-2.5% (0.8-1.0), imprecision between series (c.v.) 1.8-9.3 (0.4-9.3), recovery 99-102% (93-103). Comparison of HPLC results with results obtained using a quantitative microbiological assay yielded acceptable agreement both for serum and urine. The method was successfully used in a pharmacokinetic study with human volunteers.

A new and rapid method for monitoring the new oxazolidinone antibiotic linezolid in serum and urine by high performance liquid chromatography-integrated sample preparation

A sensitive and rapid HPLC-assay for determining the new oxazolidinone antibiotic linezolid in serum and urine is described. HPLC-integrated sample preparation permits the direct injection of serum and urine samples without any pre-treatment. The in-line extraction technique is realized by switching automatically from the extraction column to the analytical column. After the matrix has passed the extraction column the retained analyte will be quantitatively transferred to the analytical column where separation by isocratic HPLC will be performed. Linezolid is detected according to its absorption maximum at 260 nm. The quantification limits are estimated to be 0.3 and 0.5 microg/ml in serum and urine samples, respectively. The described procedure allows sample clean-up and determination of the antibiotic within 20 min, thereby facilitating drug-monitoring in clinical routine.

In situ measurement of linezolid and vancomycin concentrations in intravascular catheter-associated biofilm

We describe a new method for the measurement of antimicrobial concentrations in the biofilm associated with the endoluminal surface of intravascular catheters. We quantified endoluminal planktonic bacteria in haemodialysis catheters using the acridine orange method on catheter blood. After catheter removal, separate lumens were perfused in vitro with either vancomycin or linezolid to simulate in vivo antibiotic infusion. Biofilm was recovered using endoluminal brushes, weighed and assayed by fluoroimmunoassay for vancomycin and by bioassay for linezolid. Viable bacteria were counted by serial dilution and agar plating. Biofilm had measurable amounts of vancomycin in 11/11 catheter lumens post-infusion (0.3-18.2 mg biofilm per lumen, mean 6.8 mg; vancomycin concentration 0.2-89 mg/g biofilm, median 19 mg/g). By comparison, linezolid was detected in 4/11 catheter lumens post-infusion (0.5-18.1 mg biofilm per lumen, mean 5.9 mg; linezolid concentration 0.9-6.1 mg/g biofilm, median 1.5 mg/g). Percentage reductions in biofilm-associated bacterial counts post-antibiotic were 84-100%, median 95% (vancomycin) and 0-98%, median 91% (linezolid). We found a significant difference (P = 0.05; Wilcoxon rank sum test) in vancomycin concentrations in coagulase-negative staphylococcal biofilm (median 17.0 mg/g, mean 27.9 mg/g) compared with glycopeptide levels found in biofilm associated with other microorganisms (median 5.5 mg/g, mean 6.9 mg/g). Biofilm concentrations of vancomycin are generally higher than linezolid after antibiotic infusion, which can be explained partly by glycopeptide binding to glycocalyx. Neither antibiotic achieved consistent 100% kill of biofilm bacteria after single infusions, even when a very high concentration was present. The endoluminal brush technique can be used to measure antibiotic concentration in intravascular catheter-associated biofilm in situ. This approach can be exploited to measure biofilm antibiotic concentrations in vivo, without the need for catheter removal.

Development and validation of a high-performance liquid chromatographic method for the determination of clomazone residues in surface water

A method is described for the determination of clomazone residues in surface water by high-performance liquid chromatography with UV detection. The method involves solid-phase extraction with C18 extraction tubes. Clomazone was separated on a C18 column with a mobile phase of methanol-water (65:35, v/v) at pH 4.0 and a flow-rate of 1.0 ml/min. After optimization of the extraction and separation conditions, the method was validated. The method developed can be used for determination of clomazone in surface water, at the limit of 0.1 mcirog/l set by the European Union drinking water directive, with a 400-fold preconcentration.