High-performance liquid chromatographic determination of cloxacillin in pharmaceutical dosage forms

Identification and characterization of degradation products of dicloxacillin in bulk drug and pharmaceutical dosage forms

Impurity profiling of dicloxacillin sodium bulk drug and pharmaceutical dosage forms subjected to stability studies is evaluated. Of many impurities detected in HPLC analysis, three were not reported in the literature. The impurities have been identified by LC-MS; isolated by preparative HPLC; and characterised by NMR, Mass spectroscopy and IR. Pure impurities obtained by isolation were co-injected with dicloxacillin sodium sample to confirm the retention times in HPLC. Structure elucidation of these degradation products by spectral data has been discussed in detail.

Stability-indicating analysis of isoxazolyl penicillins using dual wavelength high-performance liquid chromatography

Stability-indicating high-performance liquid chromatography analytical procedures were developed for specific determination of four isoxazolyl penicillins during degradation under neutral and accelerated acid/alkali conditions. The chromatographic conditions were set so that the drug peak was well separated from the peaks of the degradation products. Peak homogeneity of the resolving drug peak was assessed by the shape of the ratio chromatogram. Good and reproducible separations were achieved on a reversed-phase column using a mobile phase consisting of acetonitrile and a solution of 20 mM potassium dihydrogen phosphate plus 10 mM tetramethylammonium chloride in water (adjusted to pH 5). Optimal separations for all four drugs were achieved within the range of 15-21% organic modifier in the mobile phase. The detection wavelengths were 220 nm and 240 nm. The stability-indicating nature of the methods was confirmed by the linearity of the pseudo-first order plots. The utility of dual-wavelength chromatography in establishment of stability-indicating assays is highlighted.

Hydrophobicity of beta-lactam antibiotics. Explanation and prediction of their behaviour in various partitioning solvent systems and reversed-phase chromatography

beta-Lactam antibiotics tend to undergo self-association in hydrophilic organic solvents, which leads to a strong dependence of their experimentally observable log P values on the partitioning conditions. As a result, most of the earlier obtained log P values for beta-lactam antibiotics cannot be applied as a common hydrophobicity measure, but they proved to be linearly related to each other and to a large body of reversed-phase chromatographic data. The retention of cephalosporins on reversed-phase liquid chromatographic columns is complicated by silanophilic interactions. However, under elution conditions that eliminate these silanophilic interactions, good correlations with log P data are observed, and a unified hydrophobicity scale for 90 penicillin and cephalosporin compounds could be evaluated. The Hansch and Leo additive scheme was shown to be valid for the calculation of hydrophobicities for penicillin and cephalosporin C-6(7) substituents, but it failed when applied to the prediction of cephalosporin C-3-substituent hydrophobicities. The hydrophobic increments for the sixteen most common cephalosporin C-3-substituents were empirically evaluated from literature data, and a simple equation was derived for an overall beta-lactam antibiotic hydrophobicity calculation. The proposed scale is valid for predicting the partitioning of most beta-lactam antibiotics in both hydrophilic and lipophilic organic-water systems, although it should be used with caution when applied to antibiotics containing additionally charged side-chains.

Determination of degradation products and impurities of amoxicillin capsules using ternary gradient elution high-performance liquid chromatography

A specific high-performance liquid chromatography method has been developed for the determination of amoxicillin penicilloic acids (PA), p-hydroxyphenylglycine (p-HPG), 6-aminopenicillanic acid (6-APA) and unidentified materials in amoxicillin capsules. The accuracy of the measurements was demonstrated by the standard addition technique on actual capsule samples. Within-day and between-day precision studies gave coefficients of variation of 3.15 and 1.70% for PA, 4.75 and 3.81% for p-HPG, and 5.59 and 32.23% for 6-APA, respectively. Typical calibration and expanded linearity of response curves for these components show no curvature over the range of interest. The detection limits for PA, p-HPG and 6-APA are 0.7, 0.2 and 0.6 micrograms/ml of sample extract and are considered adequate for the intended use of the method. These levels correspond to 0.35, 0.10, 0.30 mg per 500-mg Amoxil capsule, respectively.