Is chocolate in some way even more lethal to dogs than to the rest of us?

You are correct with regards to Chocolate being unsafe to consume for our companion animals. Overconsumption of chocolate can cause serious illness and perhaps death. Chocolate contains an ingredient called Theobromine. It is the ingredient that can cause harm to our dogs and cats. Dogs and cats, unlike us humans, do not possess the enzyme to break down theobromine. Therefore, theobromine accumulates within the body after time. Your pet may not be ill the first time he/she consumes chocolate but after time your pet consumes more chocolate toxicity can occur. After saying this, Bakers Dark Chocolate contains more theobromine than milk chocolate. Therefore, a toxicity to chocolate can occur more readily when consumption of Dark Chocolate than milk chocolate. It is best if Chocolate is not consumed at all.

If chocolate is consumed, the following toxicity symptoms may occur: vomiting, diarrhea, diuresis (urinary incontinence), hyperactivity, rapid breathing/heartbeat, muscle tremors, seizures, coma.

Dangerous Quantities of Chocolate:

Here are some web sites for you to peruse:

www.urbanlegends.com/animals/chocolate_and_dogs.html

www.kc.net/~wolf2dog/chocolate.htm

From Tuft’s Newsletter:

Theobromine causes different reactions to different dogs: dogs with health problems, especially epilepsy, are more affected by theobromine than healthy dogs. Theobromine can trigger epileptic seizures in dogs prone to or at risk of epilepsy. The size of the dog will also be a major factor: the smaller the dog, the more affected it is by the same amount than a larger dog. Therefore, toxicity is described on a mg/Kg basis.

Furthermore, theobromine can cause cardiac irregularity, especially if the dog becomes excited. Cardiac arythmia can precipitate a myocardial infarct which can kill the dog.

Theobromine also irritates the GI tract and in some dogs can cause internal bleeding which in some cases kills them a day or so later.

An Example:

Chocolate - active ingredient = theobromine:

* The half life in the dog is 17.5 hours

* The Toxic dose in the dog is 100-150 mg/kg.

+ A kilogram (kg) = 2.2 lbs.

+ A milligram(mg) = 1/1000 of a gram

So for a 50 lb. dog a toxic dose would be roughly 2.2 grams (2200 mg) of pure chocolate.

However the concentration of theobromine varies with the formulation of the chocolate so:

* Milk chocolate has 44mg/oz (154mg/100gm): toxic dose for 50 lb dog - 50 oz of milk chocolate.

* Semisweet chocolate has 150 mg/oz (528mg/100gm): toxic dose for 50 lb dog - 15 oz of semisweet chocolate

* Baking chocolate 390mg/oz (1365 mg/100gm): toxic dose for 50 lb dog - 5 oz of baking chocolate

Thus a dog eating one oz of baking chocolate would have to eat almost 3 oz of semisweet or 10 oz of milk chocolate to get the same dose of theobromine.