Displaying all 19 publications

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  1. Pan Y, Mak JW, Ong CE
    Biomed. Chromatogr., 2013 Jul;27(7):859-65.
    PMID: 23386533 DOI: 10.1002/bmc.2872
    In this study, a simple and reliable reverse-phase high-performance liquid chromatography (RP-HPLC) method was established and validated to analyze S-mephenytoin 4-hydroxylase activity of a recombinant CYP2C19 system. This system was obtained by co-expressing CYP2C19 and NADPH-CYP oxidoreductase (OxR) proteins in Escherichia coli (E. coli) cells. In addition to RP-HPLC, the expressed proteins were evaluated by immunoblotting and reduced CO difference spectral scanning. The RP-HPLC assay showed good linearity (r(2) = 1.00) with 4-hydroxymephenytoin concentration from 0.100 to 50.0 μm and the limit of detection was 5.00 × 10(-2) μm. Intraday and interday precisions determined were from 1.90 to 8.19% and from 2.20 to 14.9%, respectively. Recovery and accuracy of the assay were from 83.5 to 85.8% and from 95.0 to 105%. Enzyme kinetic parameters (Km , Vmax and Ki ) were comparable to reported values. The presence of CYP2C19 in bacterial membranes was confirmed by immunoblotting and the characteristic absorbance peak at 450 nm was determined in the reduced CO difference spectral assay. Moreover, the activity level of co-expressed OxR was found to be comparable to that of the literature. As a conclusion, the procedures described here have generated catalytically active CYP2C19 and the RP-HPLC assay developed is able to serve as CYP2C19 activity marker for pharmacokinetic drug interaction study in vitro.
  2. Al Azzam KM, Saad B, Aboul-Enein HY
    Biomed. Chromatogr., 2010 Sep;24(9):977-81.
    PMID: 20066730 DOI: 10.1002/bmc.1395
    Capillary zone electrophoresis methods for the simultaneous determination of the beta-blocker drugs, atenolol, chlorthalidone and amiloride, in pharmaceutical formulations have been developed. The influences of several factors (buffer pH, concentration, applied voltage, capillary temperature and injection time) were studied. Using phenobarbital as internal standard, the analytes were all separated in less than 4 min. The separation was carried out in normal polarity mode at 25 degrees C, 25 kV and using hydrodynamic injection (10 s). The separation was effected in an uncoated fused-silica capillary (75 mum i.d. x 52 cm) and a background electrolyte of 25 mm H(3)PO(4) adjusted with 1 m NaOH solution (pH 9.0) and detection at 198 nm. The method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 1-250 microg/mL for atenolol and chlorthalidone and from 2.5-250 microg/mL for amiloride. The relative standard deviations of intra- and inter-day migration times and corrected peak areas were less than 6.0%. The method showed good precision and accuracy and was successfully applied to the simultaneous determination of atenolol, chlorthalidone and amiloride in various pharmaceutical tablets formulations.
  3. Al Azzam KM, Saad B, Aboul-Enein HY
    Biomed. Chromatogr., 2010 Sep;24(9):948-53.
    PMID: 20082285 DOI: 10.1002/bmc.1390
    Capillary zone electrophoresis coupled with a capacitively coupled contactless conductivity detector (CE-C(4)D) has been employed for the determination of atenolol and amiloride in pharmaceutical formulations. Acetic acid (150 mm) was used as background electrolyte. The influence of several factors (detector excitation voltage and frequency, buffer concentration, applied voltage, capillary temperature and injection time) was studied. Non-UV-absorbing L-valine was used as internal standard; the analytes were all separated in less than 7 min. The separation was carried out in normal polarity mode at 28 degrees C, 25 kV and using hydrodynamic injection (25 s). The separation was effected in an uncoated fused-silica capillary (75 microm, i.d. x 52 cm). The CE-C(4)D method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 5-250 microg/mL for the studied analytes. The relative standard deviations of intra- and inter-day migration times and corrected peak areas were less than 6.0%. The method showed good precision and accuracy and was successfully applied to the simultaneous determination of atenolol and amiloride in different pharmaceutical tablet formulations.
  4. Al Azzam KM, Saad B, Makahleah A, Aboul-Enein HY, Elbashir AA
    Biomed. Chromatogr., 2010 May;24(5):535-43.
    PMID: 19739243 DOI: 10.1002/bmc.1323
    A micellar electrokinetic chromatography (MEKC) method for the simultaneous determination of the antiviral drugs acyclovir and valacyclovir and their major impurity, guanine, was developed. The influences of several factors (surfactant and buffer concentration, pH, applied voltage, capillary temperature and injection time) were studied. Using tyramine hydrochloride as internal standard, the analytes were all separated in about 4 min. The separation was carried out in reversed polarity mode at 28 degrees C, 25 kV and using hydrodynamic injection (15 s). The separation was effected in a fused-silica capillary 100 microm x 56 cm and a background electrolyte of 20 mM citric acid-1 M Tris solution (pH 2.75), containing 125 mM sodium dodecyl sulphate and detection at 254 nm. The method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 0.1-1 microg/mL (guanine) and from 0.1 to 120 microg/mL for both valacyclovir and acyclovir. The relative standard deviations of intra- and inter-day migration times and corrected peak areas were less than 5.0%. The proposed method was successfully applied to the determination of the analytes in tablets and creams. From the previous study it is concluded that the stability-indicating method developed for acyclovir and valacyclovir can be used for analysis of the drug in various stability samples.
  5. See KL, Elbashir AA, Saad B, Ali AS, Aboul-Enein HY
    Biomed. Chromatogr., 2009 Dec;23(12):1283-90.
    PMID: 19488980 DOI: 10.1002/bmc.1251
    A simple, rapid and validated capillary electrophoretic method has been developed for the separation and determination of ofloxacin and ornidazole in pharmaceutical formulations with detection at 230 nm. Optimal conditions for the quantitative separations were investigated. Analysis times shorter than 4 min were obtained using a background electrolyte solution consisting of 25 mmol/L phosphoric acid adjusted with 1 M Tris buffer to pH 8.5, with hydrodynamic injection of 5 s and 20 kV separation voltage. The validation criteria for accuracy, precision, linearity and limits of detection and quantitation were examined and discussed. An excellent linearity was obtained in concentration range 25-250 microg/mL. The detection limits for ofloxacin and ornidazole were 1.03 +/- 0.11 and 1.80 +/- 0.06 microg/mL, respectively. The proposed method has been applied for the analysis of ofloxacin and ornidazole both individually and in a combined dosage tablet formulation. The proposed validated method showed recoveries between 96.16 and 105.23% of the nominal contents.
  6. Elbashir AA, Saad B, Ali AS, Saleh MI, Aboul-Enein HY
    Biomed. Chromatogr., 2009 May;23(5):464-71.
    PMID: 19016231 DOI: 10.1002/bmc.1137
    A capillary zone electrophoretic method has been developed and validated for the determination of the impurity quinocide (QC) in the antimalarial drug primaquine (PQ). Different buffer additives such as native cyclodextrins and crown ethers were evaluated. Promising results were obtained when either beta-cyclodextrin (beta-CD) or 18-crown-6 ether (18C6) were used. Their separation conditions such as type of buffer and its pH, buffer additive concentration, applied voltage capillary temperature and injection time were optimized. The use of 18C6 offers slight advantages over beta-CD such as faster elution times and improved resolution. Nevertheless, migration times of less than 5 min and resolution factors (R(s)) in the range of 2-4 were obtained when both additives were used. The method was validated with respect to selectivity, linearity, limits of detection and quantitation, analytical precision (intra- and inter-day variability) and repeatability. Concentrations of 2.12 and 2.71% (w/w) of QC were found in pharmaceutical preparations of PQ from two different manufacturers. A possible mechanism for the successful separation of the isomers is also discussed.
  7. Aasim WR, Gan SH, Tan SC
    Biomed. Chromatogr., 2008 Sep;22(9):1035-42.
    PMID: 18655218 DOI: 10.1002/bmc.1073
    A stereospecific gas chromatography-mass spectrometry analysis method for amphetamine-type stimulants in human urine was recently developed. For maximum efficiency, liquid-liquid extraction and chiral derivatization of the analytes using (R)-(-)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride were performed simultaneously. The effects of (1) use of saturated sodium chloride in 2.0 M sodium hydroxide, (2) extraction solvent volume, (3) percentage of triethylamine, (4) derivatization reagent volume, (5) sample mixing time, (6) incubation temperature and (7) incubation time on method sensitivity and variability were assessed using a two-level, eight-run Plackett-Burman design followed by a fold-over design. The use of saturated sodium chloride solution and the derivatization reagent volume were significant factors (ANOVA, p<0.01). The saturated sodium chloride solution decreased sensitivity whereas an increased volume of derivatization reagent increased sensitivity. Calibration curves for all analytes were linear between 5 and 500 microg/L, with correlation coefficients of >0.99. Detection limits were
  8. Elbashir AA, Saad B, Ali AS, Saleh MI, Aboul-Enein HY
    Biomed. Chromatogr., 2009 Mar;23(3):295-301.
    PMID: 18816453 DOI: 10.1002/bmc.1113
    A capillary electrophoretic (CE) method for the baseline separation of the enantiomers of primaquine diphosphate (PQ) and quinocide (QC) (a major contaminant) in pharmaceutical formulations is proposed. Both components were separated under the following conditions: 50 mm tris phosphate buffer (pH 3.0) containing 15 mm hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD) as background electrolyte; applied voltage, 16 kV; capillary temperature, 25 degrees C; detection wavelength, 254 nm; hydrostatic injection, 10 s. The separations were conducted using a 35 cm length and 50 microm i.d. uncoated fused silica capillary column. Under the optimized conditions, the components were successfully separated in about 5 min. Intraday precision of migration time and corrected peak areas when expressed as relative standard deviation ranged from 0.17 to 0.45 and 2.60 to 3.94%, respectively, while the interday precision ranged from 2.59 to 4.20 and 3.15 to 4.21%, respectively. After the validation exercise, the proposed method was applied for the determination of QC impurity in PQ formulations.
  9. Venkatesh G, Majid MI, Ramanathan S, Mansor SM, Nair NK, Croft SL, et al.
    Biomed. Chromatogr., 2008 May;22(5):535-41.
    PMID: 18205140 DOI: 10.1002/bmc.965
    A simple, sensitive and specific reversed-phase high-performance liquid chromatographic method with UV detection at 251 nm was developed for quantitation of buparvaquone (BPQ) in human and rabbit plasma. The method utilizes 250 microL of plasma and sample preparation involves protein precipitation followed by solid-phase extraction. The method was validated on a C18 column with mobile phase consisting of ammonium acetate buffer (0.02 m, pH 3.0) and acetonitrile in the ratio of 18:82 (v/v) at a flow rate of 1.1 mL/min. The calibration curves were linear (correlation coefficient>or=0.998) in the selected range. The method is specific and sensitive with limit of quantitation of 50 ng/mL for BPQ. The validated method was found to be accurate and precise in the working calibration range. Stability studies were carried out at different storage conditions and BPQ was found to be stable. Partial validation studies were carried out using rabbit plasma and intra- and inter-day precision and accuracy were within 7%. This method is simple, reliable and can be routinely used for preclinical pharmacokinetic studies for BPQ.
  10. Chik Z, Johnston A, Tucker AT, Burn RT, Perrett D
    Biomed. Chromatogr., 2007 Aug;21(8):775-9.
    PMID: 17497758
    A fast and simple capillary zone electrophoresis method was developed and validated for the determination of lidocaine in skin using tape samples. Separation was performed in a 350 mm (265 mm to window) x 50 microm i.d. fused silica capillary using a background electrolyte of phosphoric acid-Tris pH 2.5. The extraction of lidocaine from tape samples was achieved using methanol, which was diluted to 50% with water before injection. Procaine was the internal standard. The migration times for procaine and lidocaine were 2.9 and 3.2 min, respectively. The limit of quantification for lidocaine was 50 microg, with signal to noise ratio greater than 10. The calibration curve was linear from 50 to 1000 microg with r(2) greater than 0.99. The CV for both within- and between-assay imprecision and the percentage of inaccuracy for the quality control samples including lower and upper limits of quantitation were 97%. The accuracy and selectivity of this method allowed the measurement of lidocaine in tape samples obtained from a skin tape stripping study of local anesthetics in healthy subjects.
  11. Venkatesh G, Ramanathan S, Nair NK, Mansor SM, Sattar MA, Khan MA, et al.
    Biomed. Chromatogr., 2007 May;21(5):484-90.
    PMID: 17294505
    A simple and sensitive RP-HPLC-UV method was developed and validated for simultaneous determination of atenolol and propranolol and subsequently applied to investigate the effect of dimethyl sulfoxide in rat in situ intestinal permeability studies. Atenolol (400 microm) and propranolol (100 microm) were perfused in the small intestine of anaesthetized (pentobarbitone sodium 60 mg/kg, i.p.) male Sprague-Dawley rats either in the presence (1, 3 and 5%) or in the absence of dimethyl sulfoxide. There was no significant alteration (p > 0.05) in the permeability of atenolol and propranolol, which indicated there was no effect of various concentrations of dimethyl sulfoxide (1-5%) on the membrane integrity of the rat intestinal tissues. The analytical method was validated on a C(4) column with a mobile phase comprising ammonium acetate buffer (pH 3.5, 0.02 m) and acetonitrile in the ratio of 30:70 (v/v) at a flow rate of 1.0 mL/min. The validated method was found to be accurate and precise and stability studies were carried out at different storage conditions and both analytes were found to be stable. These findings are applicable for determining the absorbability of water-insoluble drugs and new chemical entities for the purpose of classifying them in the biopharmaceutical classification system.
  12. Liew KB, Loh GO, Tan YT, Peh KK
    Biomed. Chromatogr., 2014 Dec;28(12):1782-8.
    PMID: 24788875 DOI: 10.1002/bmc.3221
    A simple, rapid, specific and reliable high-performance liquid chromatographic assay of meloxicam in human plasma has been developed using a C18 reversed-phase analytical column. Reversed-phase chromatography was conducted using a mobile phase of 0.02 potassium dihydrogen phosphate (adjusted to pH 2.7 with phosphoric acid)-acetonitrile-triethylamine (35:65:0.05, v/v) with UV detection at 354 nm. The drug in human plasma was deproteinized using a combination of methanol and chloroform. This method is simple, rapid and consistent with a high recovery of meloxicam in human plasma ranging from 93.29 to 111.09%. Regression analysis for the calibration plot for plasma standards obtained for the drug concentrations between (25-4000) ng/mL indicated excellent linearity (r ≥ 0.9997). The proposed method was applied to study the bioequivalence between Mobic (original) and Melocam (generic) products. The study was conducted on using two tablets (4 × 7.5 mg) of each of the commercial product and the reference standard in a two-way open randomized crossover design involving 20 volunteers. Area under the concentration-time curve, peak concentration (C(max)) and time to reach C(max) were 72,868.61 ng h/mL, 2133.93 ng/mL and 4.06 h for Mobic, and 78,352.52 ng h/mL, 2525.18 ng/mL and 3.61 h for Melocam. Two C(max) were discovered in the pharmacokinetic profiles which confirm enterohepatic recirculation.
  13. Sharif KM, Rahman MM, Azmir J, Khatib A, Sabina E, Shamsudin SH, et al.
    Biomed. Chromatogr., 2015 Dec;29(12):1826-33.
    PMID: 26033701 DOI: 10.1002/bmc.3503
    Multivariate analysis of thin-layer chromatography (TLC) images was modeled to predict antioxidant activity of Pereskia bleo leaves and to identify the contributing compounds of the activity. TLC was developed in optimized mobile phase using the 'PRISMA' optimization method and the image was then converted to wavelet signals and imported for multivariate analysis. An orthogonal partial least square (OPLS) model was developed consisting of a wavelet-converted TLC image and 2,2-diphynyl-picrylhydrazyl free radical scavenging activity of 24 different preparations of P. bleo as the x- and y-variables, respectively. The quality of the constructed OPLS model (1 + 1 + 0) with one predictive and one orthogonal component was evaluated by internal and external validity tests. The validated model was then used to identify the contributing spot from the TLC plate that was then analyzed by GC-MS after trimethylsilyl derivatization. Glycerol and amine compounds were mainly found to contribute to the antioxidant activity of the sample. An alternative method to predict the antioxidant activity of a new sample of P. bleo leaves has been developed.
  14. Liew KB, Loh GO, Tan YT, Peh KK
    Biomed. Chromatogr., 2014 Sep;28(9):1246-53.
    PMID: 24585432 DOI: 10.1002/bmc.3153
    The objectives of this study were to develop a new deproteinization method to extract amoxicillin from human plasma and evaluate the inter-ethnic variation of amoxicillin pharmacokinetics in healthy Malay volunteers. A single-dose, randomized, fasting, two-period, two-treatment, two-sequence crossover, open-label bioequivalence study was conducted in 18 healthy Malay adult male volunteers, with one week washout period. The drug concentration in the sample was analyzed using high-performance liquid chromatography (UV-vis HPLC). The mean (standard deviation) pharmacokinetic parameter results of Moxilen® were: peak concentration (Cmax ), 6.72 (1.56) µg/mL; area under the concentration-time graph (AUC0-8 ), 17.79 (4.29) µg/mL h; AUC0-∞ , 18.84 (4.62) µg/mL h. Those of YSP Amoxicillin® capsule were: Cmax , 6.69 (1.44) µg/mL; AUC0-8 , 18.69 (3.78) µg/mL h; AUC00-∞ , 19.95 (3.81) µg/mL h. The 90% confidence intervals for the logarithmic transformed Cmax , AUC0-8 and AUC0-∞ of Moxilen® vs YSP Amoxicillin® capsule was between 0.80 and 1.25. Both Cmax and AUC met the predetermined criteria for assuming bioequivalence. Both formulations were well tolerated. The results showed significant inter-ethnicity variation in pharmacokinetics of amoxicillin. The Cmax and AUC of amoxicillin in Malay population were slightly lower compared with other populations.
  15. Liew KB, Loh GO, Tan YT, Peh KK
    Biomed. Chromatogr., 2015 Jun;29(6):953-60.
    PMID: 25400284 DOI: 10.1002/bmc.3378
    A simple, rapid, specific and reliable UFLC coupled with ESI-MSMS assay method to simultaneously quantify sildenafil and N-desmethyl sildenafil, with loperamide as internal standard, was developed. Chromatographic separation was performed on a Thermo Scientific Accucore C18 column with an isocratic mobile phase composed of 0.1% v/v formic acid in purified water-methanol (20:80, v/v), at a flow rate of 0.3 mL/min. Sildenafil, N-desmethyl sildenafil and loperamide were detected with proton adducts at m/z 475.4 > 58.2, 461.3 > 85.2 and 477.0 > 266.1 in multiple reaction monitoring positive mode, respectively. Both analytes and internal standard were extracted by diethyl ether. The method was validated over a linear concentration range of 10-800 ng/mL for sildenafil and 10-600 ng/mL for N-desmethyl sildenafil with correlation coefficient (r(2) ) ≥0.9976 for sildenafil and (r(2) ) ≥0.9992 for N-desmethyl sildenafil. The method was precise, accurate and stable. The proposed method was applied to study the bioequivalence between a 100 mg dose of two pharmaceutical products: Viagra (original) and Edyfil (generic) products. AUC0-t , Cmax and Tmax were 2285.79 ng h/mL, 726.10 ng/mL and 0.94 h for Viagra and 2363.25 ng h/mL, 713.91 ng/mL and 0.83 hour for Edyfil. The 90% confidence interval of these parameters of this study fall within the regulatory range of 80-125%, hence they are considered as bioequivalent.
  16. Yahaya N, Sanagi MM, Abd Aziz N, Wan Ibrahim WA, Nur H, Loh SH, et al.
    Biomed. Chromatogr., 2017 Feb;31(2).
    PMID: 27474795 DOI: 10.1002/bmc.3803
    A rapid dispersive micro-solid phase extraction (D-μ-SPE) combined with LC/MS/MS method was developed and validated for the determination of ketoconazole and voriconazole in human urine and plasma samples. Synthesized mesoporous silica MCM-41 was used as sorbent in d-μ-SPE of the azole compounds from biological fluids. Important D-μ-SPE parameters, namely type desorption solvent, extraction time, sample pH, salt addition, desorption time, amount of sorbent and sample volume were optimized. Liquid chromatographic separations were carried out on a Zorbax SB-C18 column (2.1 × 100 mm, 3.5 μm), using a mobile phase of acetonitrile-0.05% formic acid in 5 mm ammonium acetate buffer (70:30, v/v). A triple quadrupole mass spectrometer with positive ionization mode was used for the determination of target analytes. Under the optimized conditions, the calibration curves showed good linearity in the range of 0.1-10,000 μg/L with satisfactory limit of detection (≤0.06 μg/L) and limit of quantitation (≤0.3 μg/L). The proposed method also showed acceptable intra- and inter-day precisions for ketoconazole and voriconazole from urine and human plasma with RSD ≤16.5% and good relative recoveries in the range 84.3-114.8%. The MCM-41-D-μ-SPE method proved to be rapid and simple and requires a small volume of organic solvent (200 μL); thus it is advantageous for routine drug analysis.
  17. Kwan SH, Ismail MN
    Biomed. Chromatogr., 2019 Aug 26.
    PMID: 31452214 DOI: 10.1002/bmc.4686
    Researchers frequently use two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) prior to mass spectrometric analysis in a proteomics approach. The i2D-PAGE method, which 'inverts' the dimension of protein separation of the conventional 2D-PAGE, is presented in this publication. Protein lysate of Channa striata, a freshwater snakehead fish, was separated based on its molecular weight in the first dimension and its isoelectric point in the second dimension. The first-dimension separation was conducted on a gel-free separation device, and the protein mixture was fractionated into 12 fractions in chronological order of increasing molecular weight. The second-dimension separation featured isoelectric focusing, which further separated the proteins within the same fraction according to their respective isoelectric point. Advantages of i2D-PAGE include better visualisation of the isolated protein, easy identification on protein isoforms, shorter running time, customisability and reproducibility. Erythropoietin standard was applied to i2D-PAGE to show its effectiveness for separating protein isoforms. Various staining methods such as Coomassie blue staining and silver staining are also applicable to i2D-PAGE. Overall, the i2D-PAGE separation method effectively separates protein lysate and is suitable for application in proteomics research.
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