- Poison(s): Chocolate contains the methylxanthine substance theobromine. Related methylxanthines are caffeine and theophylline (found in coffee and tea). Pharmaceutical xanthine preparations are available and are used primarily as bronchodilators (to widen the airways) in conditions including asthma. They also have uses in cardiovascular disease and the treatment of age related dementia. Preparations include 'Millophiline', 'Corvental' and 'Vivitonin'. Methylxanthines have a stimulant action on the central nervous system, cardiovascular and respiratory systems, causing increased alertness, and increasing blood pressure, cardiac output and breathing rate. So-called 'Dog Chocolates' do not contain cocoa solids or theobromine.
- Species affected: Many animals are sensitive to theobromine and consequently chocolate poisoning can affect most species. Dogs are particularly likely to suffer accidental poisoning by scavenging or well-intentioned but misguided 'treating' with chocolate-containing items.
- Toxic dose: the amount of chocolate required to produce a toxic effect in any given patient depends on the size of the patient and the theobromine content of the chocolate. Theobromine content is estimated from percentage cocoa solids - dark or bittersweet chocolate will have a much higher theobromine content than milk chocolate, continental chocolate also tends to be higher in cocoa solids and consequently theobromine dose. The more the cocoa content is 'diluted', the lower the potential toxicity. Consequently, a very small number of squares of dark chocolate has the potential to be dangerous in a small terrier, whereas a large labrador can probably eat several portions of milk chocolate-containing desert without ill effect.
- Symptoms: The stimulant effects of theobromine are responsible for the symptoms of chocolate intoxication. Affected animals may have increased heart rate and blood pressure and increased breathing rate. Effects may also be seen from central nervous system stimulation. This may produce tremors, twitching / nervousness, or in more severe cases seizures, loss of consciousness, and death. These symptoms may occur within hours of ingestion. Chocolate consumption can cause gastrointestinal upset. The fat content of (particularly milk) chocolate products can also cause pancreatitis (inflammation of the pancreas) which causes stomach pain, vomiting and diarrhoea, may be severe, and which will often require hospitalisation and intensive treatment. Gastrointestinal symptoms will often take a day or more to become apparent.
- Action: Contact your veterinary surgery for advice immediately if you believe your pet has consumed chocolate or chocolate-containing foods, even if they are not showing any unusual symptoms at the time. It will be helpful to your vet if you are able to provide them with the weight of the animal, the exact chocolate / foodstuff consumed, how much has been eaten, and the time that has passed since the substance was eaten (or if you do not know this precisely, for instance the box of chocolates disappeared from the coffee table while you were out of the house, the earliest and latest times that it could have occurred). If your pet is showing any symptoms, it is important to seek immediate veterinary attention - but do call ahead so that the surgery can make arrangements to see you as quickly as possible.
- Treatment: Your veterinary surgeon will attempt to estimate the total dose consumed from the information you are able to give them, and will assess whether treatment is likely to be required. They may consult a poisons information service for specialist advice. The more complete the information you can provide, the more accurate this assessment will be and unnecessary treatment may be avoided - if information is incomplete, precautionary treatment may be advised. If treatment is considered necessary, it may include induction of emesis (making the animal sick) or gastric lavage ('stomach pumping') if the chocolate has been consumed reasonably recently. Further treatment may include administration of intravenous fluids (a drip) to support the circulation, and activated charcoal to absorb theobromine from the digestive tract. Treatment may also be required for pancreatitis or more mild digestive upset, should these arise. While deaths do sometimes occur from chocolate poisoning, most cases, if seen promptly, can be treated successfully.
Perhaps fortunately, the sort of milk chocolate popular in the UK is very low in cocoa solids, so cases of serious poisoning from Dairy Milk and Mars bars are uncommon in all but the smallest dogs. Don't however underestimate the cocoa content of cakes and deserts prepared with cocoa powder. If in doubt, it's always better to seek advice early than to wait and see.
Chocolate poisoning is an unfortunate feature of the holiday seasons in veterinary practice - we see it most commonly around Christmas and Easter, though of course it can occur at any time of year. Please be careful when leaving chocolates around the house - particular in larger than usual seasonal quantities - and avoid the use of chocolate Christmas tree decorations (which are usually pretty disappointing in any case!). Please also beware the alcohol content of liqueur chocolates. Sadly, poisoning of pets by intentional 'treating' with chocolate does still occur, so continuing education of both the pet owning and general public is clearly required.