Why would a drug that damages capsules treat a viral infection

Drug that demages capsule is used to treat viral infection because Curing a viral infection  antibiotics are useless against viral infections. This is because viruses are so simple that they use their host cells to perform their activities for them. So antiviral drugs work differently to antibiotics, by interfering with the viral enzymes instead.  

Antiviral drugs are currently only effective against a few viral diseases, such as influenza, herpes, hepatitis B and C and HIV – but research is ongoing. A naturally occurring protein, called interferon (which the body produces to help fight viral infections), can now be produced in the laboratory and is used to treat hepatitis C infections.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added