Validation related substances

Non-specific absolute assay methods, e.g. volumetric titration, can be applied to avoid the establishment of a reference substance. This is only appropriate, however, when the monograph describes a separation test for related substances. This approach is certainly valid for the determination of the content of pharmaceutical raw materials but less acceptable for the assay of content of pharmaceutical preparations where the employment of specific assay methods is recommended (ICH Guideline 1994) to take account of decomposition of the active ingredient during the shelf life of the product and to avoid possible interference from excipients. 

An additional key validation criterion for early phase methods is an evaluation of solution stability to establish that the API and related substances do not degrade in the solvent system used for sample preparation. This allows for limits to be set for solution lifetime. 

Toro, L, Dulsat, J. E, Fabregas, J. L., and Claramunt, J. (2004). Development and validation of a capillary electrophoresis method with ultraviolet detection for the determination of the related substances in a pharmaceutical compound. /. Chromatogr. A 1043(2), 303 — 315. 

Sabbah, S., and Scriba, G. K. E. (2001). Development and validation of a capillary electrophoresis assay for the determination of 3,4-diaminopyridine and 4-aminopyridine including related substances./. Chromatogr. A 907(1-2), 321-328. 

Shafaati, A., and Clark, B. J. (1996). Development and validation of a capillary zone electrophoretic method for the determination of atenolol in presence of its related substances in bulk and tablet dosage form./. Pharm. Biomed. Anal. 14(11), 1547 — 1554. 

Owens, P. K., Wikstrdm, H., Nagard, S., and Karlsson, L. (2002). Development and validation of a capillary electrophoresis method for ximelagatran assay and related substance determination in drug substance and tablets.. Pharm. Biomed. Anal. 27, 587-598. 

Erythromycin, a macrolide antibiotic, lacks a significant chromophore. Detection sensitivity was enhanced by using a wavelength of 200 nm and selecting an injection solvent of lower conductivity than the BGE. In order to facilitate the separation of erythromycin and its related substances, 35% (v/v) ethanol was incorporated into a 150 mM phosphate buffer pH 7.5. Resolution of all of the compounds was achieved in approximately 45 min. The method was employed as an assay method for erythromycin and for impurity determination. Peptide antibiotics, such as colistin and polymyxin, are mixtures of many closely related compounds. A validated CZE method for impurity analysis of polymyxin B was described, employing 130 mM triethanolamine-phosphate buffer at pH 2.5 to reduce the adsorption of analyte onto the capillary wall. Methyl-/l-cyclodextrin (M-/1-CD) and 2-propanol were found to be necessary for selectivity enhancement. Using similar buffer additives, the same group developed and validated a method for colistin analysis. ... 

An MEKC method for the determination of ibuprofen, codeine phosphate hemihydrate, their nine potential degradation products, and impurities in a commercial tablet formulation was developed, optimized, and fully validated according to ICH guidelines and submitted to the regulatory authorities. The optimized system containing ACN as organic modifier allowed baseline separation of ibuprofen, codeine, and nine related substances within 12 min. 

Analytical Development of API and Drug Products. Early methods to support synthetic and formulation developments are often developed in the form of potency assay, impurities/related substance assay, dissolution, Karl Fischer, identity, chiral method, and content uniformity. These analytical methods are developed and validated in a fast and timely manner to support all phase II studies. 

METHOD VALIDATION FOR HPLC ANALYSIS OF RELATED SUBSTANCES IN PHARMACEUTICAL DRUG PRODUCTS... 

Authentic sample a purified and characterized sample of a related substance. Unlike reference standards, authentic samples may not be of high purity. However, the purity of an authentic sample has to be determined before use. Authentic samples are used in method development to identify related substances in the analysis. In addition, they are used extensively to prepare the spiked samples in method validation. 

Spiked sample a sample added with a known amount of related substances, prepared from authentic samples during method development or validation. 

System Suitability Tests. The appropriate system suitability tests should be defined before method validation (e.g., precision, resolution of critical related substances, tailing, detector sensitivity). These system suitability tests should be performed in each method validation experiments. System suitability results from the method validation experiment can be used to determine the appropriate system suitability acceptance criteria. 

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