Background Herbal medicinal products have a long-standing history of use in the therapy of common respiratory infections. We sought to assess the potential of five validated herbal extracts regarding their ability to restrict SARS-CoV-2 replication in vitro: Bronchipret thyme-ivy (BRO TI), Bronchipret thyme-primrose (BRO TP), Imupret (IMU), Sinupret extract (SINx) and Tonsipret (TOP). Methods Vero cells were incubated with different concentrations of herbal extracts and infected with SARS-CoV-2 for 48 hours. The inhibition of viral replication was assessed by determination of the viral RNA load in the cell culture supernatant using quantitative polymerase chain reaction (qPCR). Results SARS-CoV-2 RNA load was reduced by non-cytotoxic concentrations of BRO-TP (up to approximately 1,000-fold) and, to a lesser extent, IMU and TOP (approximately 10-fold). Conclusions Some herbal extracts showed a promising in vitro effectiveness against SARS-CoV-2, suggesting an antiviral potential of herbal medicinal products. The potential of herbal medicines to restrict SARS-CoV-2 and to treat COVID-19 should be investigated further in a clinical setting.

Relevance. Medicinal products of plant origin have long been successfully used in the treatment of various diseases, including those of viral etiology. Nevertheless, their effect on the replication of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has not been studied so far. Objective. To evaluate the potential of drugs based on validated plant extracts – RE (Bronchipret, Bronchipret TP, Tonsilgon N, Sinupret extract, Tonsipret) with respect to their ability to suppress SARS-CoV-2 replication in vitro. Materials and methods. Vero cells (Vero) incubated with RE of different concentrations were infected with SARS-CoV-2 virus. After 48 h the virus replication (the number of viral RNA copies in cell culture supernatant) was determined by quantitative polymerase chain reaction. Results. SARS-CoV-2 RNA copy number under the action of non-cytotoxic concentrations of Bronchipret TP decreased by 1000 times and by 10 times under the action of drugs Tonsilgon N and Tonsipret. Conclusion. Some of the studied REs in vitro demonstrated promising antiviral activity. It is advisable to conduct further, including clinical, studies of their activity against SARS-CoV-2 in the treatment of coronavirus infection (COronaVirus Disease 2019 – COVID-19).