Antifreeze contains a substance, ethylene glycol, which is very toxic to kidneys. It is also very sweet, which is the tragic reason so many pets are poisoned by it each year.
Since antifreeze is similar to alcohol, the first thing you might notice about a pet who has recently ingested it is that they stagger around like they are drunk! After that, they may seem to recover, only to develop vomiting, lethargy, and loss of appetite several hours later as IRREVERSIBLE kidney damage occurs. After the kidneys fail, the pet will become comatose and will eventually die. It does not take much antifreeze to be toxic to pets. One-half tablespoon is fatal to cats.
There is a test for antifreeze, and special medication can be give intravenously to help prevent kidney damage IF your pet is treated quickly. If you see your pet drinking antifreeze, seek veterinary treatment immediately! There is a non-toxic antifreeze, called Sierra®, which can be used safely around pets.