The active ingredient in antifreeze is ethylene glycol and due to the sweet taste dogs tend to be attracted to this liquid that drips from the radiator beneath cars. Ethylene glycol causes kidney failure in dogs real quickly. Within 30 minutes of ingestion dogs appear to be acting drunk and within 12-24 hours after ingestion full-blown kidney failure emerges and little can be done at that time.
A big part of the problem is that it takes a very small dose of ethylene glycol to be lethal for a dog (half a shot glass for a 20-pound dog or 3 cc. per pound) and it can be ingested not only by licking the liquid from the ground but also by if the dog walks in a puddle of it and then licks his paws.
In order for treatment with the antidote (called Fomepizole) to be effective, it must be administered within 5 hours of ingestion. With early recognition and timely treatment, many dogs can be saved.
The best remedy, of course, is prevention by not allowing your dog to ingest antifreeze in the first place.