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Publications (15)21.72 Total impact

  • A. Madhavi, D. V. Subba Rao, A. Naidu, P. Raghuram
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    ABSTRACT: A simple, rapid and sensitive high performance liquid chromatographic method was developed for the separation and quantification of positional isomers of zafirlukast in bulk drugs and dosage forms using a chiral column. Elution time was 20min in normal phase mode and ultra violet detection was carried out at 240nm. Efficient separation was achieved on an immobilized amylose-based Chiralpak-IA column using n-hexane/ethanol/trifluoroacetic acid/diethyl amine (65:35:0.1:0.1, v/v) as the mobile phase. Resolutions between ortho, meta and para isomers of zafirlukast were found to be >3.0. The active pharmaceutical ingredient was extracted from tablets using tetrahydrofuran. The calibration graphs for meta and para isomers of zafirlukast were linear (r 2>0.999) when ranging from the limit of quantitation to 0.3%. The method showed excellent recoveries for both zafirlukast isomers identified in bulk and formulated products. The test solution was found to be stable in the mobile phase for 48h after preparation. The developed LC method was validated with respect to linearity, accuracy, precision and robustness.
    Chromatographia 07/2009; 70(1):233-237. · 1.37 Impact Factor
  • A. Madhavi, D. V. Subba Rao, P. Srinivasu, A. Naidu
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    ABSTRACT: A novel liquid chromatographic method has been developed and validated for the determination of ranolazine, its potential four impurities in drug substance and drug products. Efficient chromatographic separation was achieved on a C18 stationary phase (150×4.6mm, 3.0microns particles) with simple mobile phase combination delivered in gradient mode at a flow rate of 1.0mLmin−1 at 210nm. In the developed method, the resolution between ranolazine and its four potential impurities was found to be greater than 2.0. Regression analysis shows an r value (correlation coefficient) greater than 0.999 for ranolazine and for its four impurities. This method was capable to detect all four impurities of ranolazine at a level below 0.004% with respect to test concentration of 1.0mgmL−1 for a 10μL injection volume. The method has shown good, consistent recoveries for ranolazine (98.8–101.1%) and for its four impurities (97.2–100.3). The test solution was found to be stable in the diluent for 48h. The drug was subjected to stress conditions. The mass balance was found close to 99.5%.
    Chromatographia 07/2009; 70(1):333-338. · 1.37 Impact Factor
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    ABSTRACT: An isocratic normal phase high-performance liquid chromatographic (NP-HPLC) method has been developed and validated for the quantitation of Z-isomer in lanoconazole. Separation was achieved with a Thermo Hypersil Silica column. The ratio of 2-propanol, n-hexane and triethylamine in the mobile phase were optimized to obtain the best separation. UV detection was performed at 296 nm. The described method is linear over a range of LOQ--15.0 microg/ml of Z-isomer. The mean recovery of Z-isomer was found to be in the range of 97-99%. The method is simple, rapid, selective, accurate and precise, useful in the quality control of bulk manufacturing.
    Journal of pharmaceutical and biomedical analysis 06/2009; 50(3):535-7. · 2.45 Impact Factor
  • A. Madhavi, A. Naidu, D. V. Subba Rao, P. Srinivasu
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    ABSTRACT: A novel liquid chromatographic method for analysis three potential impurities in brimonidine tartrate drug substance has been developed and validated. Efficient chromatographic separation was achieved on a C8 column (250mm×4.6mm, 5-μm particles) with a simple mobile-phase gradient at a flow rate of 1.0mLmin−1. Quantification was achieved by use of ultraviolet detection at 248nm. Resolution between brimonidine tartrate and its three potential impurities was greater than 3.0. Regression analysis showed the r value (correlation coefficient) was >0.999 for brimonidine and its three impurities. The method was capable of detecting all three impurities of brimonidine tartrate at levels below 0.07μg in a test concentration of brimonidine tartrate of 1.0mgmL−1 and for an injection volume of 10μL. A solution of brimonidine tartrate in acetonitrile–water 2:8 (v/v) was stable for 48h. The drug was subjected to stress conditions as prescribed by the ICH. Degradation was found to occur slightly under oxidative stress conditions but the drug was stable to aqueous, acidic, and basic hydrolysis, and photolytic and thermal stress. The assay of the stressed samples was calculated relative to a qualified reference standard and the mass balance was found close to 99.8%. The method was validated for linearity, accuracy, precision, and robustness.
    Chromatographia 06/2009; 69(11):1-7. · 1.37 Impact Factor
  • P. Radhakrishnanand, D. V. Subba Rao, V. Himabindu
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    ABSTRACT: A new and accurate chiral liquid chromatographic method has been developed for the separation of palonosetron hydrochloride (PALO) and its (R,R)-enantiomer in bulk drug samples with an elution time of about 20min. The chromatographic separation was carried out by normal phase chromatography using an immobilized cellulose based chiral stationary phase (Chiralpak-IC) with a mobile phase composed of n-hexane:ethanol:1,4 dioxane:trifluoroacetic acid:diethylamine (65:30:5:0.3:0.3, v/v) pumped at a flow rate of 1.0mLmin−1. The resolution (R s ) between the enantiomers was found to be greater than 3.0 and interestingly the (R,R)-enantiomer was eluted prior to the (S,S)-enantiomer (PALO) in the developed method. Mobile phase additives, trifluoroacetic acid and diethylamine played a key role in achieving chromatographic resolution between the enantiomers and also in enhancing chromatographic efficiency. The limit of detection (LOD) and limit of quantification (LOQ) of the (R,R)-enantiomer were found to be 0.03 and 0.1μg respectively for 10μL injection volume. The developed method shows excellent linearity (r 2>0.999) over a range of LOQ to 0.3% for the (R,R)-enantiomer. The percentage recovery of the (R,R)-enantiomer in bulk drug samples ranged from 97.2 to 102.3 revealing good sensitivity of the developed method. Robustness studies were also carried out on the developed method.
    Chromatographia 01/2009; 69(3):369-373. · 1.37 Impact Factor
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    ABSTRACT: A simple, sensitive gradient RP-LC assay method has been developed for the quantitative determination of vardenafil HCl in bulk drug and in pharmaceutical dosage forms, used to treat erectile dysfunction. The developed method is also applicable for the related substances determination. Efficient chromatographic separation was achieved on a C18 stationary phase with simple mobile phase combination delivered in a gradient mode and quantification was carried out using ultraviolet detection at a flow rate of 1.0mLmin−1. In the developed LC method the resolution between vardenafil and its four potential impurities was found to be greater than 3.0. Regression analysis shows an r 2 value (correlation coefficient) greater than 0.99 for vardenafil and its four impurities. This method was capable of detecting all four impurities of vardenafil at a level of 0.009% with respect to test concentration of 1.0mgmL−1 for a 10μL injection volume. The method has shown good and consistent recoveries for vardenafil (98.4–100.6%) and its four impurities (93.5–106.2%). The test solution was found to be stable in the diluent for 48h. Mass balance was found close to 99.4%.
    Chromatographia 10/2008; 68(9):829-835. · 1.37 Impact Factor
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    ABSTRACT: A new and accurate chiral liquid chromatographic method has been developed for the separation and quantification of (S,R,S)-enantiomer (unwanted enantiomer) and (R,R,R)-isomer (key intermediate) of aprepitant in bulk drug and formulation samples of apprepitant. The elution time was approximately 20min using an immobilized amylose-based chiral stationary phase (Chiralpak-IA). The mobile phase was n-hexane and ethanol (90:10, v/v) and was delivered at a flow rate of 1.0mLmin−1. Detection was carried out with a wavelength set to 220nm. The resolution factor between enantiomers was found to be greater than five. Limit of detection for both (S,R,S) enantiomer and (R,R,R) isomer of aprepitant was 0.035µg, and limit of quantification for both (S,R,S) enantiomer and (R,R,R) isomers of aprepitant was 0.1µg, for a 10µL injection. The developed method showed excellent linearity (r>0.999) for both isomers. When the method was applied to bulk drug samples and in pharmaceutical formulations recoveries were obtained ranging from 97.2 to 103.1%. Aprepitant sample solutions were found to be stable when characterized over a period of 48h.
    Chromatographia 09/2008; 68(7):669-673. · 1.37 Impact Factor
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    ABSTRACT: A simple, sensitive gradient RP-LC assay method has been developed for the quantitative determination of amtolmetin guacyl in bulk drug, used as anti-inflammatory drug. The developed method is also applicable for related substances determination. Efficient chromatographic separation was achieved on a C18 stationary phase with simple mobile phase combination delivered in a gradient mode and quantification was carried out using ultraviolet detection at 313 nm at a flow rate of 1.0 mL min−1. In the developed LC method the resolution between Amtolmetin Guacyl and its three potential impurities was found to be greater than 2.0. Regression analysis shows an r value (correlation coefficient) greater than 0.99 for amtolmetin guacyl and its three impurities. This method was capable to detect all three impurities of amtolmetin guacyl at a level of 0.002% with respect to test concentration of 0.5 mg mL−1 for a 10 μL injection volume. The inter- and intra-day precision values for all three impurities and for amtolmetin guacyl was found to be within 2.0% RSD at its specification level. The method has shown good and consistent recoveries for amtolmetin guacyl (99.2–101.5%) and its three impurities (94.5–104.8%). The test solution was found to be stable in diluent for 48 h. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. Considerable degradation was found to occur in oxidative stress conditions. The stress samples were assayed against a qualified reference standard and the mass balance was found close to 99.6%. The developed RP-LC method was validated with respect to linearity, accuracy, precision and robustness.
    Chromatographia 09/2008; 68(7):567-577. · 1.37 Impact Factor
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    ABSTRACT: A new and accurate chiral liquid chromatographic method has been developed for determination of the enantiomeric purity of montelukast sodium (R enantiomer) in bulk drugs and dosage forms. Normal phase chromatographic separation was performed on an immobilized amylose-based chiral stationary phase with n-hexane–ethanol–1,4-dioxane–trifluoroacetic acid–diethylamine 65:25:10:0.3:0.05 (v/v) as mobile phase at a flow rate of 1.0mLmin−1. The elution time was approximately 15min. The resolution (R S) between the enantiomers was >3. The mobile phase additives trifluoroacetic acid and diethylamine played a key role in achieving chromatographic resolution between the enantiomers and also in enhancing chromatographic efficiency. Limits of detection and quantification for the S enantiomer were 0.07 and 0.2μg, respectively, for a test concentration of montelukast sodium of 1,000μgmL−1 and 10μL injection volume. The linearity of the method for the S enantiomer was excellent (R 2>0.999) over the range from the LOQ to 0.3%. Recovery of the S enantiomer from bulk drug samples and dosage forms ranged from 97.0 to 103.0%, indicative of the high accuracy of the method. Robustness studies were also conducted. The sample solution stability of montelukast sodium was determined and the compound was found to be stable for a study period of 48h.
    Chromatographia 07/2008; 68(3):263-267. · 1.37 Impact Factor
  • D. V. Subba Rao, P. Radhakrishnanand
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    ABSTRACT: A simple stability-indicating LC method has been developed for the quantitative determination of dutasteride in bulk drug samples and in pharmaceutical dosage forms in the presence of degradation products. The retention time of dutasteride is about 7min. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. Degradation was found to occur under hydrolysis and to a lesser extent under oxidation conditions but the compound was stable to photolytic and thermal stress. The assay of stress samples was calculated against a reference standard and the mass balance was found close to 99.3%. The developed method was validated with respect to linearity, accuracy, precision and ruggedness.
    Chromatographia 04/2008; 67(9):841-845. · 1.37 Impact Factor
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    ABSTRACT: An isocratic reversed phase liquid chromatographic (RP-LC) method has been developed and subsequently validated for the determination of almotriptan malate and its process-related impurities. Separation was achieved with a Phenomenex, Gemini, C-18 column and sodium phosphate buffer (pH adjusted to 7.6): acetonitrile (80:20, v/v) as eluent, at a flow rate of 1.5 mL/min. UV detection was performed at 227 nm. The method is simple, rapid, selective, accurate and stability indicating. The described method is linear over a range of LOQ, 1.5 ug/mL (150% of the specification limit) for all the process-related impurities. The method precision for the determination of related compounds was below 1.0% R.S.D. The accuracy of the method demonstrated at 4 levels in the range of 25-150% of the specification limit and the recovery of impurities were found to be in the range of 96-102%. The method is useful in the quality control of bulk manufacturing.
    Journal of Pharmaceutical and Biomedical Analysis 04/2008; 46(4):792-8. · 2.83 Impact Factor
  • P. Radhakrishnanand, D. V. Subba Rao, V. Himabindu
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    ABSTRACT: A new and accurate chiral liquid chromatographic method has been developed for the determination of enantiomeric purity of darifenacin [(S)-enantiomer] in bulk drugs and extended release tablets. Normal phase chromatographic separation was performed on an immobilized cellulose based chiral stationary phase (Chiralpak-IC) with n-hexane:ethanol:diethylamine (50:50:0.3, v/v/v) as mobile phase at a flow rate of 1.0mLmin−1. The elution time was ~15min. The resolution (R s ) between the enantiomers was greater than four and interestingly the (R)-enantiomer was eluted prior to darifenacin in the developed method. The limit of detection (LOD) and limit of quantification (LOQ) for the (R)-enantiomer were 0.02μg and 0.07μg, respectively, for a 10μL injection volume. The method was extensively validated in terms of linearity, precision and accuracy and satisfactory results were obtained. Robustness studies were also conducted. The sample solution stability of darifenacin was determined and the compound was found to be stable for a study period of 48h.
    Chromatographia 01/2008; 68(11):1059-1062. · 1.37 Impact Factor
  • Journal of pharmaceutical and biomedical analysis. 01/2008; 46:792-798.
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    ABSTRACT: An isocratic reversed-phase liquid chromatographic method has been developed for quantitative determination of candesartan cilexetil, used to treat hypertension, in the bulk drug and in pharmaceutical dosage forms. The method is also applicable to analysis of related substances. Chromatographic separation was achieved on a 250mm×4.6mm, 5μm particle, CN column with a 50:50 (v/v) mixture of phosphate buffer, pH 3.0, and acetonitrile as mobile phase. The flow rate was 1.0mLmin−1 and the detection wavelength was 210nm. Resolution of candesartan cilexetil and six potential impurities was greater than 2.0 for all pairs of compounds. The drug was subjected to hydrolytic, oxidative, photolytic, and thermal stress and substantial degradation occurred in alkaline and acidic media and under oxidative and hydrolytic stress conditions. The major product obtained as a result of basic hydrolysis was different from that produced by acid hydrolysis and aqueous hydrolysis. The stress samples were assayed against a reference standard and the mass balance was found to be close to 99.6%. The method was validated for linearity, accuracy, precision, and robustness.
    Chromatographia 01/2007; 66(7):499-507. · 1.37 Impact Factor
  • D. V. Subba Rao, P. Radhakrishnanand, V. Himabindu
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    ABSTRACT: A stability-indicating HPLC assay method was developed for the quantitative determination of tadalafil in bulk samples and in pharmaceutical dosage forms in the presence of the degradation products. It involved a 250mm×4.6mm, 5μm C-18 column. The gradient LC method employs solution A and B as mobile phase. Solution A contains a mixture of buffer (phosphate buffer and tetra-n-butyl ammonium hydrogen sulfate) pH 2.5: acetonitrile (80:20, v/v) and solution B contains a mixture of water: acetonitrile (20:80, v/v). The flow rate was 1.0mLmin−1 and the detection wavelength was 220nm. The retention time of tadalafil is about 17min. Tadalafil was subjected to different ICH prescribed stress conditions. Degradation was found to occur in hydrolytic and to some extent in oxidative stress conditions, while the drug was stable to photolytic and thermal stress. The drug was particularly labile under alkaline hydrolytic conditions. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. The assay of stress samples was calculated against a qualified reference standard and the mass balance was close to 99.5%. The developed RP-LC method was validated with respect to linearity, accuracy, precision and ruggedness.
    Chromatographia 01/2007; 67(1):183-188. · 1.37 Impact Factor