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Chocolate Toxicity in dogs: How much is too much?

What makes chocolate toxic to dogs?
Chocolate is severely toxic to dogs because it contains a toxic compound called Theobromine (caffeine is also present in chocolate, but in much smaller amounts). This is a stimulant that affects the nervous system and heart muscle, as well as increasing the frequency of urination.
Dogs can't metabolise theobromine as effectively as humans. This allows it to build up in their system until it reaches toxic levels of concentration. This may lead to a variety of health problems including death due to cardiac arrest. Both Theobromine and Caffeine are members of a drug class called Methylxanthines.
How much dark, milk or white chocolate (if any) would dogs of various sizes need to eat before they would be at risk?
It takes a fairly large amount of Theobromine (100-150 mg/kg) to cause a toxic reaction, although there are variables to consider such as the size of dog, individual sensitivity and the concentration of the chocolate.

Using a dose of 100 mg/kg as the toxic dose:
·         1 ounce per 1 pound of body weight for Milk chocolate (low risk)
·         1 ounce per 3 pounds of body weight for Semisweet chocolate (medium risk)
·         1 ounce per 9 pounds of body weight for Baking chocolate (high risk)

Approximate Theobromine levels of different types of chocolate:
  • Dry cocoa powder contains 800 mg Theobromine per oz chocolate
  • Unsweetened (Baking) chocolate contains 390-450 mg Theobromine per oz  chocolate
  • Semisweet chocolate and sweet dark chocolate contains 150-160 mg Theobromine per oz chocolate
  • Milk chocolate contains 44-64 mg Theobromine per oz chocolate
  • White chocolate contains an insignificant source of methylxanthines.
Expected symptoms
Methylxanthines affect the nervous system; cardiovascular system and peripheral nerves. Clinical signs are most commonly seen within 12 hours of chocolate ingestion and include:
  • Hyper excitement
  • Hyper irritability
  • nervousness / trembling
  • Restlessness
  • Increased heart rate
  • Vomiting / diarrhoea
  • Excessive thirst / sometimes excessive urination (at higher levels of Theobromine toxicity)
  • Muscle spasms
  • Seizures
  • Coma (rare)
  • Death (rare) likely due to heart rhythm abnormalities.
How it is treated
If you suspect that your dog has eaten chocolate call your veterinarian for advice immediately. The toxicity of theobromine is dose dependent. This means that the size of your dog, the type of chocolate, and quantity of chocolate determine if or how toxic it is for him.
There is no specific antidote for Theobromine toxicity, medical treatment is supportive, and may include all or some of the following:
  • IV fluids - to prevent dehydration from vomiting, diarrhoea, and /or increased urination, and to flush out the theobromine from the dogs system.
  • Emetics - medications that induce vomiting. Used when the ingestion of chocolate is within 4 hours.
  • Activated charcoal - for ingestion greater than 4 hours prior to treatment, or for dogs that show continued signs of toxicity.
  • Anti-seizure medications - for dogs having seizures and/or muscle tremors.
  • Cardiac medications - for dogs exhibiting irregular heart rates or rhythms.

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