Dropsy

There is usually very little that can be done once the underlying disease reaches this stage, I'm afraid. The symptoms of dropsy occur because the fish's kidneys are failing.
eSHa 2000 does claim to cure dropsy, but it is going to depend on what exactly the underlying disease is. I can't see any medication curing a viral infection.
Some people report the use of Epsom salt baths can help. 2 teaspoons epsom salts per 4 galls ( 2 x 5ml spoons per 15 litres). It is best to use it in a quarantine tank rather than dose the whole tank. You can leave the fish in there for a few days. Epsom salts are mainly used to treat constipation, I've never tried it myself for dropsy.