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The article demonstrates that bioequivalence studies of generic drugs whose active substances are analogues of endogenous compounds found in the human body in natural concentrations present a major challenge as compared to other products and call for a specific regulatory approach. In the absence of available scientific data demonstrating that the product intake can increase the general concentration of the endogenous compound, conducting bioequivalence studies can be economically impractical in contrast to a standard comparative clinical trial, because first it would be necessary to demonstrate a significant increase in the compound concentration in blood plasma. The article analyses Russian legislation and international law with respect to evaluation of medicinal products that are analogues of endogenous compounds, i.e. vitamins, hormones, enzymes, amino acids and salts. It was demonstrated that correction for endogenous compound concentration in blood plasma and control of its dietary intake are required in order to obtain accurate bioequivalence results. The article summarises the experience gained at the FSBI «SCEEMP» of the Ministry of Health of the Russian Federation with respect to evaluation of medicines that are analogues of endogenous compounds, and outlines the most frequent mistakes in testing protocols. It substantiates the need for an individual approach tailored for each particular product, since there is no single solution to the problem of background concentration of endogenous compounds. The authors of the article developed some key solutions that can help minimize the impact of background concentrations of test samples on the results of bioequivalence assessment. Based on the results of the analysis performed and accumulated experience the authors of the article suggested some ways to resolve the problem.

Background. Optical Spectroscopic techniques widely used in practice despite the high sensitivity and wide range of studied chemical elements have the drawbacks, such as sample preparation, which is possible only in case of destruction of the investigated object. Non-destructive method to investigate the elemental composition of metal layers and other products of the shot is X-ray fluorescence spectral analysis, but the knowledge about the possibilities of modern equipment is incomplete. Objective. Identify chemical elements in damage simulator clothes at experimental shots from firearms through X-ray fluorescence spectral element analysis using a spectrometer «M4 TORNADO» manufactured by Bruker. Methods. The object of study was damaged clothe (patches of leather of jacket). Micro X-ray fluorescence spectral element analysis with a spectrometer «M4 TORNADO» manufactured by Bruker (Germany) was applied. Results. Use of technical capabilities and software spectrometer «M4 TORNADO» provides new opportunities for laboratory diagnosis of various chemical elements in the tissues of biological and non-biological origin, including shot products through micro X-ray fluorescence spectral element analysis. Its advantages over similar methods are the possibility of mapping the topography as common maps of elements, maps for individual elements and their combinations. Analyzing the distribution pattern of elements on maps researcher has an opportunity to interpret the character of layers and background concentrations of the elements by their intensity. Conclusion. Tested equipment and program software opens new opportunities for laboratory diagnostics of shot products by their X-ray fluorescence spectral element analysis., На основе использования спектрометра «M4 TORNADO» обнаружены новые возможности лабораторной диагностики продуктов выстрела путем проведения микрорентгеновского флуоресцентного спектрального элементного анализа. Его преимущества с аналогичными методами заключаются в возможности создания карт топографии, как общих карт элементов, так и отдельных элементов и их комбинаций. Наличие 10× и 100× кратных объективов предоставляет возможность проведения прицельного «микроскопического» исследования части выбранного участка за топографией элементов на карте., На основі використання спектрометру «M4 TORNADO» виявлені нові можливості лабораторної діагностики продуктів пострілу шляхом проведення мікрорентгенівського флуоресцентного спектрального елементного аналізу. Його переваги з аналогічними методами полягають у можливості створення карт топографії як загальних карт елементів, так і окремих елементів та їх комбінацій. Наявність 10× та 100× кратних об’єктивів надає можливість проведення прицільного «мікроскопічного» дослідження частини обраної ділянки за топографією елементів на карті.