With a thing like lice, I prefer 5% Sevin (carbaryl) dust. I have nothing against Ivomec, it is a great solution for a some things, but I don't like to treat animals with something that works internally (even if you apply it externally), unless it is necessary with something like burrowing mites or worms.
If you decide on Sevin, dust them once a week for several weeks, because it doesn't always kill the eggs. While Sevin is quite non toxic (keep it away from bees), I like to set the rabbits on a table with a scrap of carpet, and keep them away from their food and water when I dust. Permethrin is also supposed to be a good remedy, but I haven't used it. Absolutely don't use Malathion, or any nicotine based spray. These are good products between the DE and the Ivomec, when the former is not effective enough and the latter isn't needed.
Both of these products can also be used on cats, which are also quite sensitive to chemicals.