Dr. Greene's Answer
As a last resort for extra resistant lice, the Red Book 2000 mentions two prescription creams — Lindane and Malathion. To me these cures are worse than the disease — both for those being treated and for the environment. In fact, these creams are thought to be so dangerous in our water supply that the state of California banned the use of lindane to treat lice or scabies.
There are also several prescription oral medications currently being looked at as possible treatments. In the May 1999 issue of Infectious Diseases in Children, Septra (trimethoprim-sulfamethoxazole) is mentioned as a possible treatment for lice. The regimen is twice a day for three days with re-treatment after 7 days. There is some controversy as to whether or not it works. According to the article, it works by changing the bacteria in the gut of the louse, preventing the absorbance of vitamins. The lice then produce infertile eggs and die of malabsorption.
The Great Lice Adventure describes other techniques for getting rid of stubborn lice.