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.

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 HPLC-DAD method for simultaneous determination of febuxostat and diclofenac in biological samples: pharmacokinetic outcomes.

AIM: To develop a simple HPLC-DAD method for simultaneous determination of febuxostat (FEB) and diclofenac (DIC) in biological samples to assess pharmacokinetic outcomes of their coadministration. Methodology & results: Sample preparation was performed by liquid-liquid extraction. Drugs analysis was done on C18 column using methanol-formic acid pH 2.1 (76:24, v/v) as mobile phase and time-programmed UV detection. Lower limits of quantitation for FEB and DIC were 10 and 20 ng/ml, respectively. Baseline pharmacokinetics were similar to published data on either drug alone. Coadministration led to more than twofold increase in FEB Cmax and AUC together with a reduced hepatic uptake in rats. CONCLUSION: DIC interfered with initial distribution and terminal clearance of FEB potentially due to reduced FEB hepatic uptake.

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.

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.

The effect of a bioglass paste on enamel exposed to erosive challenge.

OBJECTIVES: The current study is evaluating the effect of using a 45S5 bioglass paste and topical fluoride application on the cross sectional micro-hardness and the chemical surface changes of eroded enamel. METHODS: Enamel discs were obtained from the buccal surface of one hundred extracted human non-carious third molars. The enamel surfaces were ground flat and each disc was coated with two layers of acid resistant nail varnish except for an exposed treatment window (3mm×2mm) on the buccal surface of the tooth. All specimens were challenged for 60 min by orange juice (Tropicana, Chicago, USA) pH 3.85+0.5. The specimens were divided into four groups: the 45S5 bioglass paste group, fluoride gel group (5 min application), fluoride gel group (24h application) while the rest of specimens served as control. The cross-sectional micro-hardness of 20 specimens from each group was measured. Five specimens from each group had their top eroded enamel surfaces examined by SEM-EDS. One-way ANOVA was used to compare the cross-sectional micro-hardness of the three groups p<0.05. RESULTS: 45S5 bioglass paste application significantly improved the sub-surface eroded enamel when compared to fluoride and control specimens (p<0.05). CONCLUSION: 45S5 bioglass paste can efficiently improve the micro-hardness of the sub-surface eroded enamel surface. CLINICAL SIGNIFICANCE: The use of the 45S5 Bioglass paste can be used efficiently as a potent remineralizing agent for the sub-surface enamel lesions resulting from erosive challenges.