Simultaneous determination of methocarbamol and aspirin in presence of their pharmacopeial-related substances in combined tablets using novel HPLC-DAD method.

Objective and Significance: Methocarbamol (MET) and aspirin (ASP) are widely used as a muscle relaxant combination. The USP reports guaifenesin (GUA) and salicylic acid (SAL) as related substances and hydrolytic products of MET and ASP, respectively. This work aimed at developing and validating a simple and sensitive RP-HPLC method for the determination of both drugs as well as their related substances (at their pharmacopeial limits) in their bulk powders, laboratory prepared mixtures, and MET-ASP combined tablets. Methods and Results: Chromatographic separation was achieved in less than 9 min with the required resolution, peak symmetry, and accuracy on C18 column using isocratic elution system of diluted acetic acid (pH 3.2): acetonitrile at the ratio of 79: 21, v/v, at a flow rate of 1 mL/min. Detection was achieved with photodiode array at 233 nm for MET, GUA, and SAL and at 273 nm for ASP. The developed method has been validated as per ICH guidelines and the calibration plots were linear over the concentration ranges of 2-150, 0.4-30, 25-450, and 0.2-27 µg/mL for MET, GUA, ASP, and SAL, respectively. Conclusion: The optimized method proved to be specific, robust and precise for the quality control of the studied drugs in pharmaceutical preparations to ascertain that their related substances are not exceeding the permitted pharmacopeial limits.

A novel voltammetry offline coupled MALDI/TOF MS characterization of electrochemical reaction products and the voltammetric determination of febuxostat in human plasma.

A simple offline coupling voltammetry-MALDI/TOF MS procedure is presented for studying electrochemical reactions. It was utilized for the characterization of the electro-reduction products of febuxostat in methanolic acetate buffer (0.1 M, pH 5). The MS analysis reveals that the carboxylic and nitrile groups are the electro-reducible groups at -0.9338 and -1.5503 V with the conversion to aldehydic and amino groups, respectively. The developed voltammetric method was validated and applied successfully for the drug determination in pharmaceutical tablets and real plasma samples within the linearity ranges 0.03-2 and 0.4-5 µg mL-1, respectively.

High-performance thin-layer chromatographic methods for the determination of febuxostat and febuxostat/diclofenac combination in human plasma.

Two simple, sensitive and specific high-performance thin-layer chromatographic (HPTLC) methods were developed for the determination of febuxostat (FEB) individually, and simultaneously with diclofenac (DIC) in human plasma. Method A presents the first HPTLC-ultraviolet attempt for FEB determination in human plasma. FEB was separated from endogenous plasma components (at hRF = 70) with ethyl acetate-methanol-water (9:2:1, v/v) mixture as mobile phase and quantified by densitometry at its λmax (315 nm). Method B is considered the first attempt for the simultaneous determination of FEB and DIC in human plasma. A mixture of petroleum ether-chloroform-ethyl acetate-formic acid (7.5:1:2.5:0.25, v/v) was used as the mobile phase. The two drugs were separated at hRF of 39 and 60 for FEB and DIC, respectively. FEB and DIC were quantified by densitometry at their isoabsorptive point (289 nm). FEB calibration plots were linear between 0.1 and 7 µg mL-1 in both methods A and B. In method B, DIC showed linear response in the range of 0.08-8 µg mL-1. Sample preparation was performed by liquid-liquid extraction using diethyl ether. Both methods did not record any interference from plasma matrix, the studied drugs' metabolites or their decomposition products. They were successfully applied for the determination of the studied drugs in healthy male volunteers after oral administration of FEB or FEB/DIC dosage forms. FEB plasma concentration increased significantly when given with DIC. The proposed methods provided very simple, rapid and cheap approaches that might be attractive for the future pharmacokinetic and bioavailability studies of FEB and/or DIC.

Derivative-ratio spectrophotometric method for the determination of ternary mixture of aspirin, paracetamol and salicylic acid.

A derivative spectrophotometric method was developed for the assay of a ternary mixture of aspirin (ASP), paracetamol (PAR) and salicylic acid (SAL). The method is based on the use of the first and second derivatives of the ratio spectra and measurement at zero-crossing wavelengths. The ratio spectra were obtained by dividing the absorption spectrum of the mixture by that of one of the components. The concentration of the other components are then determined from their respective calibration curves treated similarly. The described method was applied for the determination of these combinations in synthetic mixtures and dosage forms. The results obtained were accurate and precise.

HPTLC and Spectrophotometric Estimation of Febuxostat and Diclofenac Potassium in Their Combined Tablets.

An accurate, precise, rapid, specific and economic high-performance thin-layer chromatographic (HPTLC) method has been developed for the simultaneous quantitative determination of febuxostat (FEB) and diclofenac potassium (DIC). The chromatographic separation was performed on precoated silica gel 60 GF254 plates with chloroform-methanol 7:3 (v/v) as the mobile phase. The developed plates were scanned and quantified at 289 nm. Experimental conditions including band size, mobile phase composition and chamber-saturation time were critically studied, and the optimum conditions were selected. A satisfactory resolution (Rs = 2.67) with RF 0.48 and 0.69 and high sensitivity with limits of detection of 4 and 7 ng/band for FEB and DIC, respectively, were obtained. In addition, derivative ratio and ratio difference spectrophotometric methods were established for the analysis of such a mixture. All methods were validated as per the ICH guidelines. In the HPTLC method, the calibration plots were linear between 0.01-0.55 and 0.02-0.60 µg/band, for FEB and DIC, respectively. For the spectrophotometric methods, the calibration graphs were linear between 2-14 and 4-18 µg/mL for FEB and DIC, respectively. The simplicity and specificity of the proposed methods suggest their application in quality control analysis of FEB and DIC in their raw materials and tablets. A comparison of the proposed methods with the existing methods is presented.

Spectrophotometric determination of binary mixtures of pseudoephedrine with some histamine H1-receptor antagonists using derivative ratio spectrum method.

A derivative spectrophotometric method is developed for the assay of three binary mixtures of pseudoephedrine with fexofenadine (mix I), cetirizine (mix II) and loratadine (mix III). The method is based on the use of the first derivative of the ratio spectrum. The ratio spectrum was obtained by dividing the absorption spectrum of the mixture by that of one of the components. The concentration of the other component was determined from its respective calibration graph treated similarly. Moreover, the influence of Deltalambda for obtaining the first derivative of the ratio spectra and the effect of the divisor concentration on the calibration graphs were studied. The described method was applied for the determination of these combinations in synthetic mixtures and dosage forms. The results obtained were accurate and precise.