Unsurprisingly, the VPIS sees an increase of antifreeze (which usually contains ethylene glycol) cases during the winter months, as motorists prepare their cars for the drop in temperatures. The toxic dose for companion animals is alarmingly small and differs between cats and dogs. Given the small amount needed to cause problems, a puddle or spill of antifreeze represents a real hazard to animals, especially cats with their nocturnal ramblings and unobserved behaviours. Cats who are late presenting are often too far along the toxicological time line to be saved, as renal failure has already occurred.
The initial signs, usually present from 30 minutes onwards, include vomiting, ataxia, tachycardia and weakness. These signs are non-specific and may be missed. At 12-24 hours post exposure, cardiopulmonary signs develop, along with renal impairment and uraemia.
Ethylene glycol itself has limited toxicity, but the products of its metabolism, glycolaldehyde, glycolic acid and oxalates, are extremely toxic and so treatment is aimed at blocking the action of alcohol dehydrogenase to prevent the formation of these toxic metabolites. This is achieved by administration of the preferred substrate: alcohol (ethanol). Ideally a pharmaceutical grade of ethanol should be used. If not available, oral ethanol can be given or an IV solution made up using 40% vodka. Fomepizole is an alternative antidote, which works extremely well; however, cats require a much higher dose (6x dose) of fomepizole than dogs or humans and fomepizole is very expensive. Antidotes should not be used in animals with renal failure.