Spectrophotometric and spectrofluorimetric determination of cycloserine with p-benzoquinone

Development and validation of a selective and sensitive LC-MS/MS method for determination of cycloserine in human plasma: application to bioequivalence study

A selective and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the determination of cycloserine in human plasma is developed using niacin as internal standard (IS). The analyte and IS were extracted from 500 μL of human plasma via solid phase extraction on Waters Oasis MCX cartridges. Chromatographic separation was achieved on a Peerless Basic C18 (100 mm × 4.6mm, 3 μm) column under isocratic conditions. Detection of analyte and IS was done by tandem mass spectrometry, operating in positive ion and multiple reaction monitoring (MRM) acquisition mode. The protonated precursor to product ion transitions monitored for cycloserine and niacin were at m/z 103.1 → 75.0 and 124.1 → 80.1 respectively. The method was fully validated for its selectivity, interference check, sensitivity, carryover check, linearity, precision and accuracy, reinjection reproducibility, recovery, matrix effect, ion suppression/enhancement, stability and dilution integrity. The limit of detection (LOD) and lower limit of quantitation of the method were 0.0013 and 0.20 μg/mL respectively with a linear dynamic range of 0.20-30.00 μg/mL for cycloserine. The intra-batch and inter-batch precision (%CV) across six quality control levels was less than 8.0% for cycloserine. The method was successfully applied to a bioequivalence study of 250 mg cycloserine capsule formulation in 24 healthy Indian male subjects under fasting condition.

Colorimetric determination of gabapentin in pharmaceutical formulation

Three accurate, simple and precise colorimetric methods for the determination of gabapentin in capsules are developed. The first method is based on the reaction of gabapentin with vanillin (Duquenois reagent) in the presence of McIlvain buffer pH 7.5 and the color developed was measured at 376 nm. The linearity range was found to be 80-360 microg ml(-1). The second is based on the reaction of the primary amino group of gabapentin with ninhydrin reagent in N,N'-dimethylformamide (DMF) medium producing a colored product which absorbs maximally at 569 nm. Beer's law is obeyed in the concentration range 40-280 microg ml(-1) of gabapentin. The third method is based on the reaction of gabapentin with p-benzoquinone (PBQ) to form a colored product with lambda(max) at 369 nm. The products of the reaction were stable for 2 h at 30 degrees C, shifts of the wavelength of maximum absorbance were not observed for up to 24 h after starting the reaction. The absorbance is proportional to gabapentin concentration in the range 80-320 microg ml(-1). The optimum experimental parameters for the reactions have been studied. The validity of the described procedures was assessed. Statistical analysis of the results has been carried out revealing high accuracy and good precision. The suggested procedures could be used for the determination of gabapentin in capsules. The procedures were rapid, simple and suitable for quality control application.

Determination of cycloserine in human plasma by high-performance liquid chromatography with fluorescence detection, using derivatization with p-benzoquinone

A new method for determining cycloserine in plasma samples is described. This method is based on the derivatization of cycloserine with p-benzoquinone, a reaction that takes place at the same time as the process of plasma deproteinization due to the presence of ethanol as solvent in the solution of the derivatization reagent. Four derivatives are obtained from this reaction. The main derivative is well correlated with the cycloserine concentration. The ratio between the volumes of the plasma sample and the reagent solution is 1:2 for a p-benzoquinone concentration of 1000 microg/mL. Elution from a C18 column was isocratic, using a mobile phase containing (v/v) 85% aqueous 0.1% formic acid solution, and 15% (v/v) of a mixture of methanol and acetonitrile (1:1), with a flow-rate of 1 mL/min, at 25 degrees C. Determinations by fluorescence detection were achieved with excitation at 381 nm and emission at 450 nm, with a detection limit of 10 ng/mL for an injection volume of 5 microL. This method was validated and applied to the determination of cycloserine in blood plasma samples of several healthy volunteers.

D-cycloserine uses an active transport mechanism in the human intestinal cell line Caco 2

In a previous study we have shown that cultured epithelial cell lines can be used to measure the transepithelial passage of antimicrobial agents across the intestine and to obtain information on the mechanisms of transport utilized and predict the bioavailability of the antimicrobial agents after oral administration. In particular, among the drugs investigated, D-cycloserine had been shown to be transported in a polarized manner only in the intestinal cells. In the present work, further characterization of the transport of D-cycloserine in the human intestinal cell line Caco 2 has shown that this occurs in the apical-to-basolateral direction by an active mechanism which is energy dependent but only partially sodium dependent. Competition studies have also indicated that the transport of D-cycloserine occurs via a carrier for imino acids, amino acids with aliphatic side chains (L-Ala, D-Ala, and beta Ala), and L-Trp, L-Tyr, L-Cys, and alpha-amino isobutyric acid. This system may correspond to a proton-dependent system for L-proline and beta-alanine recently described for Caco 2 cells. In contrast with the cephalosporins, which are taken up by the Caco 2 cells via a dipeptide carrier, D-cycloserine transport cannot be inhibited by either cephalexin (a member of the class of cephalosporins) or dipeptides.

Use of p-benzoquinone for the spectrophotometric determination of certain sulphonamides

A simple spectrophotometric method for the determination of 15 sulphonamides in bulk and in dosage forms is described. The method is based on the interaction of p-benzoquinone with sulphonamides in 0.1 M hydrochloric acid. The resulting chromophore is measured at 500 nm. The effects of different variables on colour development were established. Beer's law was obeyed in a concentration range of 10-50 micrograms ml-1. Results from the analysis of different sulphonamide tablets and ophthalmic solutions marketed locally were in good agreement with that of a reference method. Correlations between A1cm(1%) and certain physical parameters such as pKa values, characteristic volume Vx, and molecular connectivity indices 1X and 1Xv were determined by linear regression equations. A poor correlation was found between A1cm(1%) and bulkiness parameters but a highly significant negative correlation was obtained with apparent pKa values.

Spectrophotometric determination of cycloserine with 9-methoxyacridine

Spectrophotometric assay for cycloserine based on the interaction of the drug with 9-methoxyacridine as a chromogenic agent is described. The highly colored substituted acridine product was identified as 9-(d-4-imino-3-isoxazolidinone)acridine. Color development was affected by time and temperature of heating and by the quantity of 9-methoxyacridine reagent utilized. The absorbance at 438 nm is linearly proportional to concentrations of cycloserine with a detection limit of 0.3 microgram/mL. The optimum range for the assay of cycloserine was from 5.0 X 10(-6) to 3.0 X 10(-4) M (correlation coefficient = 0.9999, n = 6). When applied to cycloserine capsules labeled to contain 250 mg, the proposed method gave mean recoveries of 101.84 +/- 0.48%. The procedure is sufficiently sensitive, precise, and accurate for the determination of cycloserine in its dosage form.