Using toxins to stop symptoms is a very old trick. For centuries mercury was revered as a "universal medicine" because of its symptom-stopping power. Of course it's one of the most toxic substances in the natural world. So there's nothing to explain here other than how they slapped the "antiviral" label on a drug that stops a pox.

Once you realize that no virologist even claims to be able to view any "virus" in nature, not even using an electron microscope, you may be a lot more skeptical.