**5. Conclusions**

We have shown that the both Ech, an active substance of the permitted to clinical application in Russia drugs, belonging the Histochrome series, and an antioxidant composition, containing Ech, Asc, and Toc (5:5:1), possess in vitro antiviral activity against RNA-containing tick-borne encephalitis virus and DNA-containing herpes simplex virus type 1. The studied composition of antioxidants exhibits more potent antioxidant and antiviral properties than Ech itself, thus demonstrating the synergistic effects of its components.

**Author Contributions:** S.A.F. and N.V.K. planned, summarized the work and wrote the manuscript; N.P.M. prepared echinochrome A and antioxidant composition; E.A.V. examined the antioxidant activity; E.A.P. conducted the experiments with ROS measurement; V.F.L., O.V.I., O.A.S., L.K.E. investigated the HSV-1 antiviral activity; N.V.K. and G.N.L. examined the TBEV antiviral activity.

**Funding:** This work was supported by the Ministry of Science and Education of the Russian Federation (project RFMEF161317X0076).

**Acknowledgments:** Authors are grateful to V.A.S. for constructive comments for the results and discussion of the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
