Chocolate Toxicity

Extract from Kirk and Bistner's Handbook of Veterinary Procedures and Emergency Treatment 6th edition

Sent in by Laurna McKie and Laura Potter

Chocolate's active ingredient is theobromine. The half life in a dog is 17.5 hours. The Toxic dose for a dog is 100-150 mg/kg.

A kilogram (kg) is 2.2 lbs. A milligram (mg) is equal to 1/1000 of a gram. So for a 50 pound 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), therefore the toxic dose for 50 lb dog is 50 oz of milk chocolate.
Semisweet chocolate has 150 mg/oz (528mg/100gm) therefore the toxic dose for 50 lb dog is 15 oz of semisweet chocolate
Baking chocolate 390mg/oz (1365 mg/100gm) therefore the toxic dose for 50 lb dog is 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.

The theobromine in candies consisting of chocolate that is coated over with some other substance (as in filled candies and chocolate coated dried fruits, etc.), will be more dilute than that in pure chocolate bars and solid chocolate candies.

Obviously the chocolate in milk chocolate is quite dilute and this is why many dogs can eat a piece here and there and seem not to show toxic effects, how many dogs would get hold of 50 oz at a time? This is not true of the more concentrated forms however. Dr Sue Bank's experience was that she had two dogs, a 95 pound one and a 60 pound one. They got hold of 2 one pound bags of Nestle's semi-sweet chocolate pieces (a bag each). The 95 pound dog survived but the 60 pound dog ingested a toxic dose.

The problem with feeding a dog milk chocolate as a treat is that it develops a liking for chocolate and since dogs do not seem to be as sensitive to bitter tastes as humans, it may then eat the more concentrated, and thus quite toxic, baker's chocolate if it gets a chance, or it will consume a toxic amount of milk or semi-sweet chocolate if it can get into a improperly stored supply.

Treatment which is best administered by someone with medical training follows the same strategy as treatment for caffeine overdose:
Support Respiration
Support cardiovascular function, control arrhythmia's, control electrolytes and acid-base balance.
Control CNS excitation.
Emesis
Gastric lavage
Cathartic
Activated charcoal

Administration of an activated charcoal slurry is a major component of the treatment and needs to be administered by a veterinarian, it is not a home treatment.

The following came via an e-mail

I'm sure that you all know how dangerous it is to give dogs any chocolate and especially the dark cooking chocolate. The dangerous active ingredient is theobromine. I have just learnt that the environmentally friendly cocoa shell mulch, used for gardens, contains this substance. The sacks available in the UK contain a very small notice that it may cause pets to have stomach upsets. My friend's 3-year-old Golden Retriever has just died from eating a very small quantity of the shells and his vet has written to our local paper confirming that she died of theobromine poisoning. I understand that the company who market this stuff have been ordered to put a more prominent notice on the sacks but I would hope that you would spread this warning to all dog owning friends. I have personally verified this information.

Laura Potter