Chocolate toxicity in dogs - theobromine

Theobromine is the compound in chocolate responsible for chocolate toxicity in dogs. Dogs metabolize theobromine very slowly in comparison to humans. The half life of theobromine is 17.5 hrs in dogs compared to 3 hrs in humans. Lethal toxicity in dogs is noted as 100-150 mg of theobromine per kg of body weight in dogs, though its toxic effects can be observed at much lower concentrations.

There are variables to take into account when dealing with chocolate/theobromine toxicity.

The weight of the dog.

Smaller dogs are many times more susceptible to toxicity. The ratio of mg/kg is much higher. Dogs are gorgers. Small dogs may have less body mass and weight, but can consume high amounts of chocolate if readily available.

The theobromine content in the chocolate eaten

The same amount of baker's chocolate is potentially more lethal than milk chocolate due to the content of cocoa solids. The more diluted the cocoa content in a chocolate product, the lesser the threat. This does not mean that it is ok to give dogs small amounts of chocolate. Even small amounts can lead to toxicity, even if it is not lethal. Dogs will suffer vomiting and diarreah after eating small amounts of chocolate as their body attempts to prevent further theobromine absorbtion. White chocolate is not dangerous since it does not contain theobromine. 

Beware of cocoa shell mulches used in landscaping. Cocoa shells naturally contain theobromine. Manufacturers often strip theobromine from the mulch, but not always. Check for content if your pet likes to eat the mulch.

So what happens when a dog consumes chocolate?

Theobromine stimulates the Central Nervous System (CNS). The dog shows signs of hyperactivity and restlessness, increased urine output, and irregular heartbeat. According to the Merck Veterinary Manual, Methylxanthines like theobromine increase intracellular calcium levels that lead to increased strength and contractility of skeletal and cardiac muscle. They compete for receptors in the CNS and inhibit esterases that result in increased cyclic AMP levels. They also increase circulating levels of epinephrine and norepinephrine. In severe cases, these chemical changes cause dogs to have tremors and seizures, hypertension, increased body temperature, and difficulty breathing. Coma and death may also result.

Other species are also susceptible to theobromine including cats and rabbits. However, other species are less prone to consume chocolate. Seek veterinary care immediately if you suspect your pet has ingested chocolate.