KS and Acyclovir

Question

If KS is caused by a herpes virus (HHV-8), why is Acyclovir, which is used for treatment of HHV-1 and HHV-2, of no value in treating KS?

Answer

KS is indeed caused by a herpesvirus. However, the structure of herpesvirus-8 is different enough than HHV-1 and HHV-2 (the herpes which causes cold sores and genital herpes) that it just doesn't respond to acyclovir. Oh how we all wish that acyclovir would work Drugs usually target very very specific areas in the viruses which they attack. Only a minor change in the target area is required to make the virus inpenetrable by a drug.