Simultaneous voltammetric sensing of levodopa, piroxicam, ofloxacin and methocarbamol using a carbon paste electrode modified with graphite oxide and ß-cyclodextrin.

A carbon paste electrode (CPE) was modified with graphite oxide (GrO) and ß-cyclodextrin (CD) to obtain a sensor for simultaneous voltammetric determination of levodopa (LD), piroxicam (PRX), ofloxacin (OFX) and methocarbamol (MCB). The morphology, structure and electrochemical properties of the functionalized GrO were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, contact angle measurements and cyclic voltammetry. Under the optimal experimental conditions, the sensor is capable of detecting LD, PRX, OFX and MCB by square wave voltammetry (SWV) at working potentials of +0.40, +0.60, +1.03 and + 1.27 V (versus Ag/AgCl), respectively. Response is linear from 1.0 to 20 µM for LD, from 1.0 to 15 µM for PRX, from 1.0 to 20 µM for OFX, and from 1.0 to 50 µM for MCB. The respective limits of detection are 65, 105, 89 and 400 nM. The method was successfully applied to the simultaneous determination of LD, PRX, OFX and MCB in (spiked) real river water and synthetic urine samples, and the results were in agreement with those obtained using a spectrophotometric method, with recoveries close to 100%. Graphical abstract Schematic presentation of a novel electroanalytical method employing a carbon paste electrode modified with graphite oxide and ß-cyclodextrin for the simultaneous determination of levodopa, piroxicam, ofloxacin and methocarbamol in urine and river water samples by square wave voltammetry.

Inhibition of pseudoperoxiadse activity of human red blood cell hemoglobin by methocarbamol.

After red blood cells lysis, hemoglobin is released to blood circulation. Hemoglobin is carried in blood by binding to haptoglobin. In normal individuals, no free hemoglobin is observed in the blood, because most of the hemoglobin is in the form of haptoglobin complex. In some diseases that are accompanied by hemolysis, the amount of released hemoglobin is higher than its complementary haptoglobin. As a result, free hemoglobin appears in the blood, which is a toxic compound for these patients and may cause renal failure, hypertensive response and risk of atherogenesis. Free hemoglobin has been determined to have peroxidase activity and considered a pseudoenzyme. In this study, the effect of methocarbamol on the peroxidase activity of human hemoglobin was investigated. Our results showed that the drug inhibited the pseudoenzyme by un-competitive inhibition. Both Km and Vmax decreased by increasing the drug concentration. Ki and IC50 values were determined as 6 and 10mM, respectively. Docking results demonstrated that methocarbamol did not attach to heme group directly. A hydrogen bond linked NH2 of carbamate group of methocarbamol to the carboxyl group of Asp126 side chain. Two other hydrogen bonds could be also observed between hydroxyl group of the drug and Ser102 and Ser133 residues of the pseudoenzyme.

Smart manipulation of ratio spectra for resolving a pharmaceutical mixture of Methocarbamol and Paracetamol.

Two smart, specific, accurate and precise spectrophotometric methods manipulating ratio spectra are developed for simultaneous determination of Methocarbamol (METH) and Paracetamol (PAR) in their combined pharmaceutical formulation without preliminary separation. Method A, is an extended ratio subtraction one (EXRSM) coupled with ratio subtraction method (RSM), which depends on subtraction of the plateau values from the ratio spectrum. Method B is a ratio difference spectrophotometric one (RDM) which measures the difference in amplitudes of ratio spectra between 278 and 286 nm for METH and 247 and 260 nm for PAR. The calibration curves are linear over the concentration range of 10-100 µg mL(-1) and 2-20 µg mL(-1) for METH and PAR, respectively. The specificity of the developed methods was investigated by analyzing different laboratory prepared mixtures of the two drugs. Both methods were applied successfully for the determination of the selected drugs in their combined dosage form. Furthermore, validation was performed according to ICH guidelines; accuracy, precision and repeatability are found to be within the acceptable limits. Statistical studies showed that both methods can be competitively applied in quality control laboratories.

Extraction of methocarbamol from human plasma with a polypyrrole/multiwalled carbon nanotubes composite decorated with magnetic nanoparticles as an adsorbent followed by electrospray ionization ion mobility spectrometry detection.

In this work, a polypyrrole/multiwalled carbon nanotubes composite decorated with Fe3 O4 nanoparticles was chemically synthesized and applied as a novel adsorbent for the extraction of methocarbamol from human plasma. Electrospray ionization ion mobility spectrometry was used for the determination of the analyte. The properties of the magnetic-modified adsorbent were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform IR spectroscopy, and X-ray diffraction. The effects of experimental parameters on the extraction efficiency of the sorbent were investigated. Under the optimized conditions, the linear dynamic range was found to be 2-150 ng/mL with the detection limit of 0.9 ng/mL. The relative standard deviation was 5.3% for three replicate measurements of methocarbamol in plasma sample. The extraction efficiency of the sorbent for the determination of different drugs with various polarities was also compared to that of Fe3 O4 -polypyrrole and Fe3 O4 -multiwalled carbon nanotubes sorbents. Finally, the method was used for the determination of methocarbamol in blood samples.

Trapping of muscle relaxant methocarbamol degradation product by complexation with copper(II) ion: spectroscopic and quantum chemical studies.

Structural properties of methocarbamol (Mcm) were extensively studied both experimentally and theoretically using FT IR, (1)H NMR, UV-Vis., geometry optimization, Mulliken charge, and molecular electrostatic potential. Stability arises from hyper-conjugative interactions, charge delocalization and H-bonding was analyzed using natural bond orbital (NBO) analysis. Mcm was decomposed in ethanol/water mixture at 80°C to guaifenesin [(RS)-3-(2-methoxyphenoxy)propane-1,2-diol] and carbamate ion [NH2COO(-)], where the degradation mechanism was explained by trapping the carbamate ion via the complexation with copper(II) ion. The structure of the isolated complex ([Cu(NH2COO)2(H2O)]⋅4H2O) was elucidated by spectral, thermal, and magnetic tools. Electronic spectra were discussed by TD-DFT and the descriptions of frontier molecular orbitals and the relocations of the electron density were determined. Calculated g-tensor values showed best agreement with experimental values from EPR when carried out using both the B3LYP and B3PW91 functional.

Simultaneous determination of paracetamol and methocarbamol in human plasma By HPLC using UV detection with time programming: application to pharmacokinetic study.

BACKGROUND: A combination of methocarbamol (MET) and paracetamol (PAR) is a widely used treatment approach. It provides complementary modes of action for treatment of pain associated with muscle spasm. The aim of this work was to develop and validate a new sensitive and reproducible isocratic reversed phase HPLC-UV detection method for simultaneous determination of MET and PAR in human plasma for the routine use in a therapeutic drug monitoring and pharmacokinetic laboratories. METHODS: A simple HPLC assay was developed and validated for the simultaneous determination of the above-mentioned drugs in small samples of human plasma (0.25 mL). After protein precipitation with methanol, satisfactory separation was achieved on a Hypersil® BDS C18 column (250 mm × 4.6 mm, 5 µm) using a mobile phase comprising 20 mM sodium dihydrogen phosphate buffer (pH=3) and methanol at a ratio of 80:20, v/v; the elution was isocratic at ambient temperature with a flow rate of 1.2 ml/min. The UV detector was programmed at 254 nm for 7.0 min to measure PAR and IS and at 272 nm for the subsequent 3 min to measure MET. RESULTS: Linearity was demonstrated over the concentration range from 0.02 to 20 µg/ml (mean R(2) = 0.9998, n = 10). The observed within- and between-day assay precision ranged from 1.11 to 9.4 and 2.46 to 10.0% for PAR and MET, respectively; whereas, accuracy varied between 95.2-101% and 93.9-102.2% for PAR and MET, respectively. Mean drug recovery was 99.8 for PAR and 99.0% for MET. PAR and MET were stable in frozen plasma over a period of 3 months at -80 °C. CONCLUSIONS: The validated method was applied successfully to a bioequivalence study of PAR/MET (500/400 mg) fixed dose combination tablet in healthy volunteers (n=24).

Rationally designed molecularly imprinted polymers for selective extraction of methocarbamol from human plasma.

Molecularly imprinted polymers (MIPs) with high selectivity toward methocarbamol have been computationally designed and synthesized based on the general non-covalent molecular imprinting approach. A virtual library consisting of 18 functional monomers was built and possible interactions between the template and functional monomers were investigated using a semiempirical approach. The monomers with the highest binding scores were then considered for additional calculations using a more accurate quantum mechanical (QM) calculation exploiting the density functional theory (DFT) at B3LYP/6-31G(d,p) level. The cosmo polarizable continuum model (CPCM) was also used to simulate the polymerization solvent. On the basis of computational results, acrylic acid (AA) and tetrahydrofuran (THF) were found to be the best choices of functional monomer and polymerization solvent, respectively. MIPs were then synthesized by the precipitation polymerization method and used as selective adsorbents to develop a molecularly imprinted solid-phase extraction (MISPE) procedure before quantitative analysis. After MISPE the drug could be determined either by differential pulse voltammetry (DPV), on a glassy carbon electrode modified with multiwalled-carbon nanotubes (GC/MWNT), or high performance chromatography (HPLC) with UV detection. A comparative study between MISPE-DPV and MISPE-HPLC-UV was performed. The MISPE-DPV was more sensitive but both techniques showed similar accuracy and precision.

Simultaneous spectrophotometric determination of diclofenac potassium and methocarbamol in binary mixture using chemometric techniques and artificial neural networks.

In this study, the simultaneous determination of diclofenac potassium (DP) and methocarbamol (MT) by chemometric approaches and artificial neural networks using UV spectrophotometry has been reported as a simple alternative to using separate models for each component. Three chemometric techniques-classical least-squares (CLS), principal component regression (PCR), and partial least-squares (PLS)-along with radial basis function-artificial neural network (RBF-ANN) were prepared by using the synthetic mixtures containing the two drugs in methanol. A set of synthetic mixtures of DP and MT was evaluated and the results obtained by the application of these methods were discussed and compared. In CLS, PCR, and PLS, the absorbance data matrix corresponding to the concentration data matrix was obtained by the measurements of absorbances in the range 260-310 nm in the intervals with Δλ = 0.2 nm in their zero-order spectra. Then, calibration or regression was obtained by using the absorbance data matrix and concentration data matrix for the prediction of the unknown concentrations of DP and MT in their mixtures. In RBF-ANN, the input layer consisting of 251 neurons, 9 neurons in the hidden layer, and 2 output neurons were found appropriate for the simultaneous determination of DP and MT. The accuracy and the precision of the four methods have been determined and they have been validated by analyzing synthetic mixtures containing the two drugs. The proposed methods were successfully applied to a pharmaceutical formulation containing the examined drugs.

Spectrofluorometric determination of methocarbamol in pharmaceutical preparations and human plasma.

A simple, sensitive and rapid spectrofluorometric method for determination of methocarbamol in pharmaceutical formulations and spiked human plasma has been developed. The proposed method is based on the measurement of the native fluorescence of methocarbamol in methanol at 313 nm after excitation at 277 nm. The relative fluorescence intensity-concentration plot was rectilinear over the range of 0.05-2.0 µg/mL, with good correlation (r=0.9999), limit of detection of 0.007 µg/ mL and a lower limit of quantification of 0.022 µg/ mL. The described method was successfully applied for the determination of methocarbamol in its tablets without interference from co-formulated drugs, such as aspirin, diclofenac, paracetamol and ibuprofen, The results obtained were in good agreement with those obtained using the official method (USP 30).The high sensitivity of the method allowed the determination of the studied drug in spiked human plasma with average percentage recovery of 99.42 ± 3.84.

Electrochemical determination of methocarbamol on a montmorillonite-Ca modified carbon paste electrode in formulation and human blood.

Utilizing the fascinating strong adsorptive ability, high chemical and mechanical stability properties of montmorillonite-calcium (MMT-Ca) clay, a MMT-Ca modified carbon paste electrode was developed for the sensitive determination of methocarbamol. Methocarbamol has been oxidized in buffered solutions at the developed MMT-Ca-modified CPE in a single 2-electron irreversible anodic peak. A simple and sensitive square-wave adsorptive anodic stripping voltammetric method was optimized for determination of methocarbamol in bulk form, pharmaceutical formulation and in spiked human serum using the developed modified CPE. This was carried out without the necessity for samples pretreatment and/or time-consuming liquid-liquid or solid-phase extraction steps prior to the analysis. The developed electrode exhibited an excellent sensitivity and selectivity towards methocarbamol even in the presence of 10(2)-10(4)-fold of its active ingredient "ibuprofen," common excipients, common metal ions or co-administrated drugs. Limits of detection of 3 x 10 (-9) and 1.2 x 10(-8) M and limits of quantitation of 1 x 10(-8), and 4 x 10(-8) M methocarbamol were achieved in the bulk form and in spiked human serum, respectively. Moreover, the developed method was successfully applied for determination of methocarbamol in human plasma of subjects following administration of an oral dose of Ibuflex tablets.

Muscle relaxant activity of methocarbamol enantiomers in mice.

Documented studies support the emerging idea that drug enantiomers could have different pharmacological activity. Our bibliographical data have shown that so far no report has been published on the pharmacological activity of individual enantiomers of methocarbamol. This study was conducted to characterize the muscle relaxant activity of methocarbamol enantiomers. The rotarod test was used to compare the muscle relaxant activity of racemic methocarbamol and pure enantiomers after intraperitoneal administration of the enantiomers to mice. The results show that (+)-R-methocarbamol has higher muscle relaxant activity compared with racemic methocarbamol or (-)-S-methocarbamol.

A new HPLC technique for the separation of methocarbamol enantiomers.

We have developed a stereoselective high-performance liquid chromatography technique for analytical separation of methocarbamol enantiomers. Precolumn derivatization was performed at room temperature using (-)-menthylchloroformate as a chiral reagent in the presence of pyridine as catalyst. The resulting diastereomers were separated on two Resolve C18 columns connected in series. The mobile phase was phosphate buffer (pH 7.5)-acetonitrile (50: 50, v/v) at a flow rate of 1 mL min(-1). UV detection was set at 274 nm. The optimum amount of reagent and the maximum peak intensity of the diastereomers were determined. The resolution of the diastereomers was satisfactory (alpha = 1.04) under the conditions used.

Methocarbamol degradation in aqueous solution.

The kinetics of the hydrolysis of methocarbamol to the corresponding diol guaifenesin in aqueous solution was studied. Methocarbamol was rather stable in acidic media but easily hydrolyzed in alkaline solution. The formation of an unknown compound, proved to be an isomer of methocarbamol [the 3-(2-methoxyphenoxy)-propanediol 2-carbamate] is involved. The amounts of methocarbamol and the two degradation products resulting from storage of methocarbamol in various buffer solutions over a pH range of 8.0 to 10.0 at 70-80 degrees C (ionic strength, 0.5 M), were followed as a function of time by a reversed-phase HPLC stability-indicating method to clarify the degradation pathway of methocarbamol in alkaline solutions. Analysis of the concentration-time profiles reveals that base-catalyzed methocarbamol hydrolysis proceeded mainly through the formation of its isomer. The observed degradation rates followed approximately pseudo-first-order kinetics at constant pH and temperature.

[Determination of methocarbamol]. / Oznaczanie karbaminianu gwajamaru.

Method of determination of 3-(2-metoxyfenoxy)-1,3-propandiol (Methocarbamol) with Marquisa reagent was verified. New method of quantitative determination based on the coloured reaction with Ce (IV) ion was developed.