By Brennen McKenzie, MA, MSc, VMD, cVMA

Some of the most common clinical presentations seen in general practice are gastrointestinal symptoms, such as vomiting and diarrhea. Dogs, in particular, commonly come to the veterinarian with mild acute vomiting. The potential causes for vomiting are numerous, and they range from self-limiting to life-threatening. This leads to frequent, sometimes heated debates, about when such cases should have a diagnostic workup and which tests should be chosen. I will save my thoughts on this subject for another time.

Mild acute vomiting is commonly treated empirically in practice without a definitive diagnosis, and the purpose of this column is to discuss some of the more common symptomatic treatments used.

This is a frustrating subject for the evidence-based clinician because there are innumerable treatment options, and most are largely or entirely opinion-based. This does not mean we have to give up entirely on a rational or evidence-based approach, but it requires us to set a very low level of confidence for or against common available interventions.

Treatment categories

The categories of empirical treatments used for mild acute vomiting include dietary modifications, pharmaceuticals (e.g. anti-emetics and gastroprotectants), and many others.^1-3 A well-established tradition is an initial period of fasting followed by feeding small, frequent meals with some modification of the macronutrient content of the diet. If this sounds vague, it is! Every clinician has his or her own variation on the approach to which we are often strongly attached based entirely on habit and clinical experience.

The concept of fasting to "rest" the gastrointestinal tract is intuitively appealing and scientifically dubious. It is true presenting food to a patient with ongoing nausea and vomiting may exacerbate these symptoms, but once these are controlled, there are no proven benefits to fasting. Evidence in humans supports enteral feeding to manage acute gastroenteropathy.^4,5 Pre-clinical evidence in dogs and cats and research in cases of parvoviral enteritis also suggests fasting is unlikely to be beneficial.^6-9

Feeding patterns for acute gastroenteropathy have not been systematically evaluated or compared. The feeding of small, frequent meals is rational given the changes in gastrointestinal motility often seen in affected patients and the potential for large meals to trigger further vomiting. However, it should be noted there are no comparative studies in patients with naturally occurring mild acute gastroenteropathies to indicate the optimal feeding pattern.^1,3

The recommended macronutrient composition of foods given to the acute vomiting patient is also based largely on theoretical considerations. Restricting fat and fiber is typically recommended since both can delay gastric emptying. A highly digestible, low-residue diet is commonly employed, using either commercial or homemade cooked diets.^1-3 There is negligible published clinical research evidence to support this strategy or compare different feeding strategies for acute vomiting.

Opinions also vary on the indications for anti-emetic therapy. Many clinicians will automatically give anti-emetic medications to any patient presenting for vomiting in whom they suspect a self-limiting gastroenteropathy. Others will delay such therapy until some arbitrary frequency or intensity of vomiting is exhibited. Again, it is rational to consider more aggressive treatment for more aggressive symptoms, but there is little evidence to indicate what specific clinical indicators should be used to decide when to employ antiemetic treatments,¹⁰ and most dogs with emesis appear to recover without intervention.¹¹

Drug therapies

There is at least some research available (finally!) evaluating anti-emetic drug therapies, though the quality and quantity of studies is still generally weak. The pathways leading to vomiting, and the targets for specific pharmacologic interventions, are well-described.¹⁰

There is no single "best" anti-emetic, but there is reasonable evidence to support the use of many, including: maropitant, metoclopramide, ondansetron or dolasetron, and phenothiazines such as chlorpromazine. Each treatment has its own pros and cons, and selection of specific drugs depends on specific characteristics of each case and clinician preference.^1,2,12,13

As an illustration, phenothiazines are often avoided in outpatients due to their potential for causing sedation and hypotension, but they may be used for refractor vomiting in more closely monitored inpatients.

In another example, there is some evidence suggesting metoclopramide and ondansetron may be more effective in treating nausea than maropitant, though the evidence is inconsistent. On the other hand, ondansetron may slow GI motility, which could potentially exacerbate ileus, and maropitant may have visceral analgesic properties.

The relative efficacy of these drugs may vary with the cause of vomiting, which, of course, is often not known in the case of mild acute vomiting managed in the outpatient setting, and strict or universal criteria for choosing one over the other are not supportable.^3,10,12-14

Gastroprotectants are commonly used empirically to treat mild acute vomiting. These drugs are intended to elevated gastric pH and protect the stomach lining from ulceration. However, it is not clear hyperacidity or ulceration are present in cases of acute vomiting or that these treatments have any therapeutic benefits in these patients. Many cases of acute vomiting are identified as "gastritis," and the presence of hyperacidity or damage to the lining of the stomach are assumed, but there is negligible research evidence to support these assumptions or the use of gastroprotectants in these patients.^15,16

Some dogs with vomiting may have concurrent gastroesophageal reflux (GER) or underlying disease, which may benefit from treatment with gastroprotectant medications, but this is typically unknown in most cases. Gastroprotectants do not have meaningful effects in reducing nausea or vomiting, and it is not appropriate to use them as treatments for these symptoms.

When there is a reasonable probability of GER, gastric hyperacidity, or mucosal ulceration, and gastroprotectants are indicated, there are several classes to choose from. Once again, there is very limited evidence to support the clinical efficacy of most commonly used drugs.

Antacids, such as aluminum or calcium salts, likely have minimal benefits. Histamine type-2 receptor antagonists, such as famotidine, due have some effect on gastric pH, but they are likely inferior to proton pump inhibitors (PPI), such as omeprazole and pantoprazole, and they may reduce the effectiveness of PPIs if given concurrently.

There is also very little evidence to support the purported benefits of sucralfate in protecting against gastroesophageal ulceration or shortening the duration of mild, self-limiting nausea, and vomiting.^1,3,15,16

Finally, there is essentially no meaningful evidence speaking to the efficacy of the numerous over-the-counter and home remedies sometimes employed for acute vomiting. Probiotics may have some benefit for diarrhea, but the scant evidence available does not suggest they are likely to reduce acute nausea and vomiting symptoms.¹⁷ Prokinetics, such as cisapride, might have a role in cases where gastrointestinal motility if decreased, and vomiting associated with motion may be ameliorated by maropitant and dimenhydrinate, but there is little clinical trial research on such therapies in cases of acute vomiting.³

The bottom line is acute vomiting is one of the most common clinical presentations in small animal medicine, and there are numerous therapies in common use, which most clinicians believe are reliably effective. However, almost all of the management strategies for this condition are based on the weakest of evidence: pathophysiologic rationale and anecdotal experience.

It is entirely possible, even likely, the majority of these patients would recover spontaneously without any therapy at all. At best, the value of the treatments we employ may be in reducing discomfort and possibly shortening the course of symptoms for some patients. At worst, these therapies are mere placebos for us and our clients in most of the patients we treat.

Brennen McKenzie, MA, MSc, VMD, cVMA, discovered evidence-based veterinary medicine after attending the University of Pennsylvania School of Veterinary Medicine and working as a small animal general practice veterinarian. He has served as president of the Evidence-Based Veterinary Medicine Association and reaches out to the public through his SkeptVet blog, the Science-Based Medicine blog, and more. He is certified in medical acupuncture for veterinarians. Columnists' opinions do not necessarily reflect those of Veterinary Practice News.

References

1. Elwood C, Devauchelle P, Elliott J, et al. Emesis in dogs: a review. J Small Anim Pract. 2010;51(1):4-22. doi:10.1111/j.1748-5827.2009.00820.x
2. Lawrence Y. Symptomatic management of primary acute gastroenteritis. Today's Vet Pr. 2015:46-52.
3. Trepanier LA. Rational therapy for vomiting in dogs and cats.Pacific Veterinary Conference. San Francisco; 2018. http://www.vetmed.wsu.edu/depts-VCPL/drugs.aspx. Accessed June 18, 2021.
4. Sandhu BK, European Society of Paediatric Gastroenterology, Hepatology and Nutrition Working Group on Acute Diarrhoea. Rationale for early feeding in childhood gastroenteritis. J Pediatr Gastroenterol Nutr. 2001;33 Suppl 2:S13-6. doi:10.1097/00005176-200110002-00003
5. Isolauri E, Juntunen M, Wiren S, Vuorinen P, Koivuls T. Nutritional management modifies the intestinal permeability changes in acute gastroenteritis. Pediatr Res. 1988;24(3):415-415. doi:10.1203/00006450-198809000-00085
6. Cave N. Dietary approaches to gastrointestinal disroders- Acute gastroenteritis. In: WSAVA Annual Congress. 2010.
7. Batchelor DJ, Devauchelle P, Elliott J, et al. Mechanisms, causes, investigation and management of vomiting disorders in cats: a literature review. J Feline Med Surg. 2013;15(4):237-265. doi:10.1177/1098612X12473466
8. Will K, Nolte I, Zentek J. Early enteral nutrition in young dogs suffering from haemorrhagic gastroenteritis. J Vet Med A Physiol Pathol Clin Med. 2005;52(7):371-376. doi:10.1111/j.1439-0442.2005.00745.x
9. Mohr AJ, Leisewitz AL, Jacobson LS, Steiner JM, Ruaux CG, Williams DA. Effect of early enteral nutrition on intestinal permeability, intestinal protein loss, and outcome in dogs with severe parvoviral enteritis. J Vet Intern Med. 2003;17(6):791-798. doi:10.1111/j.1939-1676.2003.tb02516.x
10. Elwood C, Devauchelle P, Elliott J, et al. Emesis in dogs: a review. J Small Anim Pract. 2010;51(1):4-22. doi:10.1111/j.1748-5827.2009.00820.x
11. Hubbard K, Skelly BJ, McKelvie J, Wood JLN. Risk of vomiting and diarrhoea in dogs. Vet Rec. 2007;161(22):755-757. doi:10.1136/vr.161.22.755
12. Kenward H, Elliott J, Lee T, Pelligand L. Anti-nausea effects and pharmacokinetics of ondansetron, maropitant and metoclopramide in a low-dose cisplatin model of nausea and vomiting in the dog: a blinded crossover study. BMC Vet Res. 2017;13(1):244. doi:10.1186/s12917-017-1156-7
13. Ramsey D, Fleck T, Berg T, et al. Cerenia Prevents Perioperative Nausea and Vomiting and Improves Recovery in Dogs Undergoing Routine Surgery. Vol 12.; 2014. http://www.jarvm.com/articles/Vol12Iss3/Vol12 Iss3McCall.pdf. Accessed June 18, 2021.
14. Hay Kraus B. Spotlight on the perioperative use of maropitant citrate. Vet Med Res Reports. 2017;Volume 8:41-51. doi:10.2147/VMRR.S126469
15. Webb C, Twedt DC. Canine gastritis. Vet Clin North Am Small Anim Pract. 2003;33(5):969-985, v-vi. doi:10.1016/s0195-5616(03)00052-4
16. Marks SL, Kook PH, Papich MG, Tolbert MK, Willard MD. ACVIM consensus statement: Support for rational administration of gastrointestinal protectants to dogs and cats. J Vet Intern Med. 2018;32(6):1823-1840. doi:10.1111/jvim.15337
17. Herstad HK, Nesheim BB, L'Abée‐Lund T, Larsen S, Skancke E. Effects of a probiotic intervention in acute canine gastroenteritis – a controlled clinical trial. J Small Anim Pract. 2010;51(1):34-38. doi:10.1111/j.1748-5827.2009.00853.x