Dr Pat is correct the best option is emergency vet care for your dog if your own vet is not available for off hours care.
You can read here about this toxin and its side effects and the care given for it
http://www.veterinarypartner.com/Content.plx?P=A&A=1423&S=1
there is no direct antidote but there is supportive care which may help a dog through the exposure. It sounds like you have started care but that the dog isn't doing well so the best option is more in person care.
This site may help you locate an emergency vet if you need one
http://www.vetlocator.com/hotline.php
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics