Hi, There is an article on wikipedia... don't know how usefull it is because some things on wikipedia aren't very good.
this is the article copied and pasted - Dogs that have ingested foods containing high levels of xylitol (greater than 100 milligram of xylitol consumed per kilogram of bodyweight) have presented with low blood sugar (hypoglycemia) which can be life-threatening.[31] Low blood sugar can result in a loss of coordination, depression, collapse and seizures in as soon as 30 minutes.[32][33] Intake of very high doses of xylitol (greater than 500 – 1000 mg/kg bwt) has also been implicated in liver failure in dogs, which can be fatal.[34] These are points of controversy, however, as earlier World Health Organization studies using much higher doses on dogs for long periods showed no ill effect.[35] A study published in the Journal of Veterinary Pharmacology and Therapeutics involved two groups of 8 Pekingese dogs fed either 1 or 4 g/kg of xylitol. In addition to developing hypoglycemia, all of the dogs developed elevation of liver enzymes associated with liver damage. The dogs also developed reduced serum phosphorus and potassium and increased serum calcium.
I just searched xylitol on wikki and it came up with the article which then if you scroll down it says about dogs. Hope he is ok