Ack! Where was this posted before? Quick treatment is imperative.
Fluid therapy (oral and/or subcutaneous -- under the skin), as with most ailments, is good here, it will help flush out the toxins. And I'm pretty sure I've seen advice from Dana Krempels about thwarting the neurological effects -- the main problem with Frontline is neurological, the rabbits treated with the stuff will often start having seizures days after the application -- by keepingthe bunny alert and active, and I believe she also suggestedtrying acupuncture.
PS: Please make sure this is noted in our rabbit savvy vet listings.