It is difficult to develop antiviral medicines.Becaseu the viruses have no metabolism of their own.So killing a virus is difficult.
It is considered intermediate between living and nonliving.
If a virus is a living organisms it is easier to kill a living organism.If an organism is dead already , we cant kill it any more .Right?
As viruses are intermediate between living and non living , it is not easy to destroy them.
That is why it is difficult to develop medicines for viruses.