Ondansetron (Zofran, Glaxo Pharmaceuticals) is a potent antiemetic drug that has proven to be very effective in both humans and animals for control of severe vomiting. It has been used in human cancer patients undergoing cisplatin therapy, a drug that frequently causes nausea and severe vomiting, with dramatic results. Ondansetron acts as a selective antagonist of serotonin S3 receptors (a principal mediator of the emetic reflex). S3 receptors are found primarily in the CTZ, on vagal nerve terminals, and in the gut in enteric neurons. The principal site of action of ondansetron is in the area postrema, but it also has some peripheral gastric prokinetic activity.
In my experience, ondansetron has produced dramatic results in either controlling or at least significantly decreasing the frequency of vomiting in dogs and cats with frequent or severe vomiting, including in dogs with severe parvovirus enteritis, in pancreatitis patients, and cats with hepatic lipidosis. The recommended dose is 0.25 to 0.5 mg/lb IV given as a slow push every 6 to 12 hours (based on patient response). Frequently dogs that appear quite distressed due to nausea and vomiting look much more relaxed and comfortable within 15 minutes of receiving ondansetron. There are no reports of any significant side effects such as diarrhea, sedation, or extrapyramidal signs in human and animal trials. While Zofran was quite expensive for many years, it came off patent in 2007 and is now affordable for use at any small animal hospital. Its use should be considered in any patient with intractable vomiting (maropitant and dolasetron are the other top choices for this situation). Animals with significant liver disease are best managed with ondansetron or dolasetron, as maropitant must be used with caution in animals with significant hepatic dysfunction.
It is best to treat animals with frequent severe vomiting aggressively in order to significantly decrease the frequency of vomiting and to enhance patient comfort. Oftentimes early use of more aggressive therapy in controlling severe vomiting, in conjunction with other therapy, will hasten an earlier positive response and a shorter hospital stay, with a lower hospital bill than if the patient is allowed to linger too long while it receives less than effective therapy.
Not sure what time. I fed her at 2am and then again at 6:30am so it had to be in-between those two feedings. This is the 2nd night in a row Ive woken up to throw up.I wonder why shes doing it overnight, but not during the day?
Good luck, and I look forward to your posts. 
