Bilious vomiting syndrome (also called reflux gastritis) can happen to cats, but is most commonly seen in dogs. The dog vomits not food or mucus, but just bile. It just looks like white, yellow or tan foam. The dog usually has an empty stomach when he or she begins to vomit, which may be one reason why dogs with the syndrome often vomit first thing in the morning.
According to VetConnect.com, dogs that are most prone to developing bilious vomiting syndrome are middle-aged or older dogs. Also, dogs that have had digestive problems like gastritis or duodenitis are also more prone to developing this syndrome. This can happen in both sexes and all breeds, including mongrels.
There are a variety of reasons why a dog could develop bilious vomiting syndrome. This could be from an injury, a complication from another digestive illness in the dog or problems with the stomach being able to handle normal stomach bile. Another reason is that the stomach lining was permanently injured after suffering a digestive illness, and that makes it try to expel any bile.
If the dog is otherwise behaving normally, then there may be no need for medication. Try feeding the dog a snack at night to see if that stops the dry heaves. But if the dog is showing other symptoms, then a vet's help is needed. Treatment usually includes a nightly dose of cimetidine, ranitidine or carafate to help soothe the stomach lining. Ethromycin may also be administered.
In order to be sure of the cause, usually a stool sample is needed to rule out other problems, and then a biopsy is performed on the stomach. The dog has to be under anaesthesia for this. VetConnect.com notes that nowadays, instead of a biopsy, a tiny camera can be sent into the stomach (an endoscopy) so the vet can examine the stomach that way.
According to Dog Owner's Home Veterinary Handbook, vomiting up bile on an empty stomach is also one of the symptoms of giardiasis, or internal parasites. Usually, this is also accompanied by weight loss and diarrhoea, but not always. If the dog is chronically vomiting bile every day, then the vet should be called immediately.