Agreed, Levamisole is the med of choice, but not at the dosage rate stated in the link posted above.
A couple of interesting articles that you might be interested in reading with regards to the dosage rate suggested when treating fish for nematodes (worms) using Levamisole HCl.
http://edis.ifas.ufl.edu/fa091
http://www.loaches.com/Members/shari2/levamisole-hydrochloride-1
It appears that the scientific community considers 2ppm of Levamisole HCl to be an adequate dosage, which works out to 1gr per 100 gallons,
not 5gr per 100 gallons as constantly reported on the internet.
The 5gr dosage rate originates from Charles Harrison, who is a chemist/ fish hobbyist, that sells Levamisole HCl, not a VMD that specializes in treating tropical fish. (such as Dr. Roy Yanong)
http://fishweb.ifas.ufl.edu/Yanong/Yanong.htm
Dr. Yanong also suggests that the treatment duration be 24 hrs, not 3 days as currently suggested by Charles Harrison. It appears that Charles got his info from a killi hobbyist (Ken Laidlaw), that as far as I can tell has no real qualifications for treating fish for disease etc beyond the hobbyist level. Also, originally Charles/Ken recommended only treating for 24 hrs, not 3 days. (then repeating 2-3 weeks later)
If what Dr. Yanong states is correct (and in my experience it is), many people use FAR more medication than required. This is most likely why some people state online that Levamisole treatments were hard on their fish, and the fish showed visible signs of stress during treatment.
Good luck.