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Relationships between R M values and mobile phase composition have been examined for six fibrate-type drugs — bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil. They were separated in horizontal chambers on RP18 plates by use of mobile phases containing phosphate buffer and different amounts of six modifiers — acetone, acetonitrile, dioxane, isopropanol, methanol, and tetrahydrofuran. Plates were visualized under UV irradiation at λ = 254 nm, and scanned with a densitometer in multi-wavelength scan mode. Optimum modifier concentrations were also investigated on RP8 and CN plates for comparison. The linearity of relationships between R M and modifier volume fraction, molar fraction, and the logarithm of the molar fraction was calculated. Most results fitted the Snyder-Soczewiński equation with r > 0.95; for almost half r > 0.99. Separation of all the drugs was achieved on RP18 plates with mobile phase containing 70% dioxane in pH 7.60 phosphate buffer.

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Relationships between R M values and mobile phase composition have been determined for the six antihyperlipidemic agents-bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil. The drugs were separated on silica gel, CN, and Diol plates using mobile phases containing n -hexane as weakly polar diluent and five polar modifiers: acetone, dioxane, ethyl methyl ketone, ethyl acetate, and tetrahydrofuran. The optimum mobile phases were also investigated on alumina, NH 2 , and polyamide phases for comparison. The linearity of relationships between R M and modifier volume fraction, molar fraction, and logarithm of molar fraction was calculated. Plates were developed in horizontal chambers, visualized under UV irradiation at λ = 254 nm, and scanned with a densitometer in the multi-wavelength scan mode. Most results fitted the Snyder-Soczewinski equation with r > 0.9; for approximately half r > 0.99. Separation of all the drugs was achieved on Diol plates with mobile phases containing 20–30% of each modifier in n -hexane, and with hexane-acetone, 9 + 1, on CN plates. Five drugs were separated using the same mobile phases on silica gel. The best separation was obtained on Diol plates with tetrahydrofuran-hexane, 2 + 8, as mobile phase.

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Authors: Łukasz Komsta, Robert Skibiński, Anita Iwańczyk and Hanna Hopkała
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Authors: Wojciech Markowski, Katarzyna Czapińska, Genowefa Misztal and Łukasz Komsta

Conditions have been established for separation of six fibrate drugs by automatic multiple development (AMD). The best system was selected by using results from systematic investigation of relationships between R M values and mobile-phase composition. The drugs were separated by multiple development on diol plates with tetrahydrofuran-hexane as mobile phase. The results of multiple development analysis predicted by computer simulation were compared with experimental results.

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Authors: Łukasz Komsta, Robert Skibiński, Anita Iwańczyk and Genowefa Misztal

The normal-phase thin-layer chromatographic behavior of five statin-like drugs — atorvastatin, cerivastatin, fluvastatin, lovastatin, and simvastatin — has been investigated. Chromatograms on silica gel, diol, and CN layers were developed with binary mobile phases containing hexane and a polar modifier in different proportions. The R F values obtained with all the mobile phases were then used to calculate Snyder-Soczewinski equations, assuming linear dependence of R M on the volume fraction of the mobile phase modifier, on the mole fraction of the modifier, and on their logarithms. The correlation between regression coefficients within and between models were investigated in depth. The coincidence between regression coefficients were also investigated by calculating Spearman’s rank correlation, and the similarity between modifiers was also checked by use of dendrograms.

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A new spectrodensitometric method was developed for the simultaneous determination of a quaternary mixture of antihyperlipidemics containing niacin, atorvastatin, and bezafibrate with either ezetimibe or simvastatin. Densitometric analysis was carried out using high-performance thin-layer chromatographic (HPTLC) silica gel 60G F254 plates as the stationary phase. The plates were developed with benzene—ACN—n-butanol (7:2:1, v/v) + 1.50%, v/v, glacial HOAC in absorbance mode at 242 nm. The retention factors of niacin, atorvastatin, bezafibrate, ezetimibe, and simvastatin were 0.17, 0.38, 0.51, 0.65, and 0.66, respectively. The method was validated according to the United States Pharmacopeia and National Formulary (USP 31—NF 26) and the International Conference on Harmonization (ICH) guidelines. Linearity ranges of all studied drugs were found to be in the range of 15–650 ng band−1 with correlation coefficient values of 0.9975 or more. Limits of detection and quantitation were 5–50 and 15–150 ng band−1, respectively. Upon applying polynomial regression to the same concentration ranges of standard solutions of all investigated drugs as well as spiked bezafibrate samples to rabbit plasma, correlation coefficient values had greatly improved. The proposed method was successfully applied for the simultaneous determination of the studied antihyperlipidemic drugs in plasma and in their pharmaceutical formulations. The developed method was utilized to study the pharmacokinetic behavior of bezafibrate and its drug—drug interaction with atorvastatin in rabbit males. This study has proven the increased myotoxicity risk upon coadministration of atorvastatin with bezafibrate.

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The retention factor R F is used in several criteria generally known as chromatographic response functions (CRF). In TLC and HPTLC most of these are based on differences between the retention factors of two substances, which are summed or multiplied. There are also other functions, for example the multispot response function ( MRF ) which enables the quality of a separation to be estimated. Although good CRF criteria should have well-defined distribution and range, current criteria based on the differences do not satisfy this requirement. Only MRF has a clearly defined range (0 to 1), but its distribution is unstable. In this paper two new independent coefficients: R U (retention uniformity) and R D (retention distance) are proposed; these always have values within the range 0 to 1 and stable density, irrespective of the number of compounds separated. Their reliable mathematical properties have been tested in wide range by Monte-Carlo simulations. An example is given of their use in the separation of fibrate-type antihyperlipidemic drugs by normal and reversed-phase TLC (114 systems).

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antihyperlipidemic drugs was necessary to achieve the treatment goals in plasma lipid levels. A low dose of statins in combination with EZE achieves comparable or even greater LDL cholesterol reduction than a very-high-dose of statins [ 1 ]. Different LC

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