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Background: The aim of this study was to perform an in vitro evaluation of the antiviral activity of several well-known organic substances against infectious bronchitis virus (IBV), the prototype strain of the coronavirus family. The new betacoronavirus SARS-CoV-2 caused COVID-19 and is the fifth pandemic of respiratory disease since the 1918 flu pandemic. There is an urgent need to find new antiviral drugs against respiratory coronaviruses but also to study the antiviral effect of well-known substances in order to identify new therapeutic approaches for people with COVID-19. Methods: The cytotoxic effect of organic substances was evaluated on a monolayer of cell culture baby hamster kidney (BHK)-21. Cultivation, accumulation, and determination of the infectious titer of IBV by cytopathic action were performed using cell cultures of chicken embryo fibroblasts and BHK-21. The antiviral effect of a substance was assessed by measurement of its chemotherapeutic index across three regimens of substance administration: (1) 2 h before infection, (2) simultaneously with infection, and (3) 2 h after infection. Results: This study's results were established in vitro. All the substances showed antiviral activity in the range of nontoxic concentrations in prophylactic regimen. Of the substances tested, 4-aminobutyric acid was the least toxic. Conclusions: Effective inhibition of virus reproduction in preventive and treatment regimens indicated that 4-aminobutyric acid and 6-aminocaproic acid affected the early stages of coronavirus reproduction. 6-aminocaproic acid hydrochloride and 7-aminoheptanoic acid may potentially also affect the early stages of coronavirus reproduction, which requires further in-depth study. [ABSTRACT FROM AUTHOR]