Valentine's Day and Easter are occasions associated with our consumption of more chocolate than usual! While we can eat chocolate all the year round and not be too concerned about the quantities, chocolate is toxic for dogs and in some cases can be fatal.
All types of chocolate are not equal! (To a chocoholic, that's stating the obvious.) The main toxic ingredient of chocolate is theobromine, but the concentration of theobromine varies with the formulation of the chocolate. White chocolate contains theobromine, but in such small amounts that poisoning is unlikely to occur. Milk chocolate has 154mgs of theobromine per 100gms of chocolate, semisweet (dark eating) chocolate has 528mgs of theobromine per 100gms of chocolate and dark cooking chocolate has 1365mgs per 100gms of chocolate. From these figures, it can be seen that cooking chocolate contains about nine times more theobromine than milk chocolate. The concentration of chocolate in different brands of chocolate varies, and if chocolate is coating another confectionery or occurs in other forms, it might vary from the above estimations. Generally, however, the concentration of theobromine in dark chocolate is substantially higher than in milk chocolate. One other important thing about dogs is that they metabolise and detoxify theobromine very much less efficiently than we do, such that the half-life of theobromine in dogs is much longer - about 17.5 hours.
The most-often-quoted toxic dose of theobromine in dogs is 100-150gms/kg bodyweight, and mild to moderate signs of toxicity have been reported at doses as low as 20mg/kg. So, in a typical scenario of chocolate poisoning, for say a 10kg dog, usually the lethal dose of theobromine is 1000mgs to 1500mgs, or 1 - 1.5gms …not very much! If the 10kg dog ate 100gms of dark cooking chocolate, the chances of it dying if left untreated would be very high, but signs of toxicity may start to appear at the 20mg/kg stage, or after it has eaten only about 20gms of chocolate. There is greater leeway for milk chocolate, but still the quantity of milk chocolate at which signs of poisoning may occur is only about 180gms for a 10kg dog. So don't become complacent and think that a little bit of chocolate will not be harmful. Dogs tend to develop a taste for chocolate, and they will not discriminate between dark and milk chocolate, and it will probably be the whole packet that goes if they decide to help themselves!
The signs of chocolate poisoning in dogs are often seen an hour or two after ingestion and may last from 12 - 36 hours. One usually sees restlessness, anxiety, hyperactivity and vomiting, which may progress to panting, fast heart rate, muscle tremors, heart arrhythmias and seizures followed by death.
If you suspect chocolate poisoning in your dog, consult your veterinarian as soon as possible. The treatment may include the induction of vomiting, a stomach washout, repeated doses of activated charcoal for four to six hours, intravenous fluids, bladder catheterisation and treatment for seizures and heart arrhythmia. If treated before seizures and heart arrhythmias start, then the outlook is good, but after this, the prognosis becomes guarded.
David Marchant BVSc PhD
The Ark Veterinary Surgery
589 Robinson Rd
Aspley Qld 4034