Validated stability-indicating HPLC method for the determination of pridinol mesylate. Kinetics study of its degradation in acid medium

Concurrent Determination of Pridinol, Diclofenac and Impurity A by HPLC-UV

A reversed-phase high-performance liquid chromatography method was developed and validated for the simultaneous determination of pridinol, diclofenac and diclofenac-related compounds in tablet formulations. The proposed method is also suitable for content uniformity determination, for dissolution test and for stability studies. Separation was achieved on a base-deactivated silica C8 column, using 50 mM phosphate buffer (pH 2.5) and methanol (40:60 v/v) as mobile phase, at a flow rate of 1.0 mL/min and column temperature of 40°C. Ultraviolet detection was made at 225 nm. The method was validated for specificity, accuracy, precision (intraday and interday levels) and linearity for each analyte. For diclofenac impurity A, sensitivity was also studied. The method showed specificity and linearity (R2: 0.999 for the three analytes) over the assessed concentration range (diclofenac: 2.5-75.0 μg/mL, pridinol: 2.0-60.0 μg/mL and impurity A: 1.25-5.0 μg/mL) and demonstrated good precision as reflected by the low coefficient of variation in all cases. Recovery rates obtained were 99.81, 100.58 and 100.96% for diclofenac, pridinol and impurity A respectively, and for all three analytes, the variances of the concentrations tested were equivalent. The detection and quantitation limits for impurity A were 0.078 and 0.261 μg/mL, respectively.

Pharmaceutical impurities and degradation products: uses and applications of NMR techniques

Current standards and regulations demand the pharmaceutical industry not only to produce highly pure drug substances, but to achieve a thorough understanding of the impurities accompanying their manufactured drug substances and products. These challenges have become important goals of process chemistry and have steadily stimulated the search of impurities after accelerated or forced degradation procedures. As a result, impurity profiling is one of the most attractive, active and relevant fields of modern pharmaceutical analysis. This activity includes the identification, structural elucidation and quantitative determination of impurities and degradation products in bulk drugs and their pharmaceutical formulations. Nuclear magnetic resonance (NMR) spectroscopy has evolved into an irreplaceable approach for pharmaceutical quality assessment, currently playing a critical role in unequivocal structure identification as well as structural confirmation (qualitative detection), enabling the understanding of the underlying mechanisms of the formation of process and/or degradation impurities. NMR is able to provide qualitative information without the need of standards of the unknown compounds and multiple components can be quantified in a complex sample without previous separation. When coupled to separative techniques, the resulting hyphenated methodologies enhance the analytical power of this spectroscopy to previously unknown levels. As a result, and by enabling the implementation of rational decisions regarding the identity and level of impurities, NMR contributes to the goal of making better and safer medicines. Herein are discussed the applications of NMR spectroscopy and its hyphenated derivate techniques to the study of a wide range pharmaceutical impurities. Details on the advantages and disadvantages of the methodology and well as specific challenges with regards to the different analytical problems are also presented.

Validation of Simultaneous Volumetric and HPLC Methods for the Determination of Pridinol Mesylate in Raw Material

Simple, sensitive, and economical simultaneous volumetric and HPLC methods for the determination of pridinol mesylate in raw material have been developed. The volumetric method is based on the reaction of pridinol with sodium lauryl sulphate in diluted sulphuric acid. Dimethyl yellow was used as indicator to detect the end point of the titration in aqueous/organic layer. The HPLC method for the determination of pridinol mesylate employs a reverse phase C18 column at ambient temperature with a mobile phase consisting of acetonitrile: 0.05 M potassium dihydrogen phosphate, pH adjusted to 5.0 (1 : 2, v/v). The flow rate was 0.8 mL/min. Quantitation was achieved with UV detection at 258 nm based on peak area. Both methods were found to be suitable for the quality control of pridinol mesylate in raw material.

Determination of pKa and forced degradation of the indoloquinoline antimalarial compound cryptolepine hydrochloride

The study was aimed at determining the acid dissociation constant of cryptolepine hydrochloride and its degradation under stressed conditions. The pKa was determined using buffers in the pH range 10.4-11.6 by spectrophotometry at controlled measurement temperature (20 ± 0.5°C). The stability of the compound was investigated under various stressed conditions including neutral, acid, alkaline, light, dry heat and oxidation at different temperatures. Degradation products were analysed by HPLC. The calculated pKa values (uncorrected and corrected for ionic strength) were 11.09 ± 0.03 and 10.99 ± 0.05, respectively. A graphical approach yielded an uncorrected pKa value of 11.07. Degradation of the compound in water, 0.1 M HCl, 0.1 M NaOH and 3% hydrogen peroxide followed a first order reaction. With proper temperature control and maintenance of uniform ionic strength, a reproducible pKa of cryptolepine is obtainable by spectrophotometry. The compound was found to be highly susceptible to oxidation and relatively stable in neutral and acidic conditions but less so in a basic medium. There were no significant changes in concentration of samples exposed to light and dry heat at 60°C over the study period.