it is difficult to make antiviral medicines than making antibiotics.
An antibacterial is a compound or substance that kills bacteria or slows their growth. Whereas, antiviral medicine aims at the viral infection. Viruses do not have their own cellular machinery and depends on its host, so there are less virus specific targets to aim at. The viruses have a high rate of mutation. Therefore, developing antiviral medicine is more difficult than developing an anti bacterial medicine.
Hope this helps,
All viruses donot have common biochemical proceess
Thus it is difficult for making anti viral medicines