I don't know much about this, so I googled around. This is a pretty good story:
Camallanus Worms: An Aquariasts Worst Nightmare
According to that article, an alternative treatment is metronidazole & praziquental. <Although he had no luck with it ... he did use it only in the water.> This 2 meds together is supposed to be the most effective anti-parasitic in the goldies world. You can find both in Jungle's anti-parasite food. This is the 1st drug I use for internal parasites. Feeding the drug containing food will get the drug directly to the worms & should be more effective than just having it in the water. <I am assuming that you will be treating the fish in a hospital setup, so that any worms/eggs in the water can be dealt with seperately .... perhaps with potassium permaganate? I know bleach will do it, but that kills your biofilter ....>
You might be able to get Levamisole from a vet. It is a prescription drug, although it is no longer listed in my (Canadian) 2009 CPS Drug reference.