Antibiotics have properties that interfere with the biochemical activities within the bacterial cell. They may prevent replication or cell respiration, possibly by inhibiting enzymatic processes, or they may damage the bacterial walls, causing lysis.
There are many different antibiotics, and therefore many different modes of action.
They all inhibit the processes within the living bacterial cell. Anti - Biotic ! Anti - Life !
Viruses are not alive (by the usual definitions of life) therefore cannot be 'killed.'
Whether they are DNA viruses or RNA viruses they 'hijack' the mechanisms within the host cell (the victim of viral attack) and use it to replicate more virus. High levels of antibiotic applied to the host cell would probably do more damage to the host cell than to the virus.
Damaging the host cell would prevent the virus from using that cell to replicate... but it would leave the host damaged, and the virus free to infect another cell/organism.
Therefore, antibiotics are not used to treat the viral infection, but are often given to control any subsequent bacterial infection which may occur.
I should add that there are classes of organism which exhibit properties halfway between viruses and bacteria, and novel 'antibiotics' may have some action against them. But this is a specialist and quickly evolving area - please consult the latest medical literature on this subject.