The studying of the drugs interaction is a pressing problem in practical medicine and pharmacy that requires additional investigation of the nature of its influence on the biological activity of pharmacological substances and on the organism of a patient. To study the nature of the interaction we have synthesized compounds that are products of interactions of metronidazole with metal salts, which are components of drugs. Investigation of structures of the obtained compounds was carried out by IR spectrometry using infrared spectrometer with Fourier transformation Tensor 27 «Bruker» (Germany). The changes in the infrared absorption spectra indicate changes in the structure of metronidazole in the cases of interaction of metal cations. It confirms obtaining of new compounds. During the research it was established that metronidazole behaves like a bidentate ligand. Specifically, for the samples of Metronidazole-Mg, Metronidazole-Al, Metronidazole-Fe2+ and Metronidazole-Bi it was established that the metronidazole is associated with metal cation via the nitrogen atom, which is located in the third position of the imidazole cycle, and through the oxygen atom of the hydroxy group. The results, obtained in the study of the Metronidazole-Ca and Metronidazole-Fe3+ samples, indicates a slightly different nature of the interaction that needs further study.