Conference Proceedings, (2016). American College of Veterinary Internal Medicine, Denver:
IMPORTANCE OF NUTRITION
Anorexia is one of the most common clinical signs of disease in cats presenting to the veterinary hospital. Unfortunately it is nonspecific and a thorough medical workup is required to determine the underlying cause. Nutritional support is critical during the period of time that the primary problem is being sought and addressed. Management of acute and chronic dysrexia should not be overlooked in the management of feline patients. Assessment of nutrition should be performed in every patient and assisted intervention should be instituted in patients that have had inadequate food intake for longer than 3–5 days (including the time before presentation to the veterinary clinic).1 Adequate caloric support is crucial for ill or injured patients. Poor body condition is associated with decreased prognosis in several species and has a negative effect on immune function, wound healing and strength.2 Additionally, poor appetite is perceived by owners as a significant quality of life concern and anorexia in companion animals can cause emotional distress to owners.3
Specially formulated diets have been shown to benefit patients affected by several disease processes, but are irrelevant if rejected. Therefore a key therapeutic target for these patients should be the maintenance of appetite and food intake. Common chronic disorders that may be nutritionally managed include: dental disease, diabetes mellitus, hyperlipidemia, obesity, gastrointestinal disorders, pancreatitis, liver disorders, kidney disease, dermatopathies, urolithiasis, osteoarthritis, cognitive disorders, and hyperthyroidism.4
ASSESSMENT OF NUTRITION: THE 5TH VITAL SIGN
A nutritional assessment including body weight, body condition score, muscle condition score, adequacy of caloric intake (including open ended questions about how the pet is eating), and a complete dietary history (including pet food, treats, supplements and items used to give medications) should be obtained. A nutritional plan should be performed for every patient for both acute and chronic illness. Awareness of these parameters and tools for assessment have been made available due to a global nutritional initiative by WSAVA.5 www.wsava.org/nutrition-toolkit.
THE UNIQUE FELINE
Cats have a higher requirement for protein and amino acids than other species. When nutrition is inadequate, energy is derived from mobilization of amino acids from muscles stores as opposed to fat.2 Elderly cats are also unique in comparison to other species as they have stable to increased level of metabolism, as opposed to decreased metabolism.6 A reduced ability to digest protein and fat has been documented in elderly cats. These combined factors make the utilization of high quality, easily digestible food product critical for these patients.7
WHAT IF THEY WON’T EAT IT?
Environmental Factors and Food Choices
As cats are particularly sensitive to environmental factors, suggestions for appetite enhancement include: quiet environment with exclusive access without interference from bothersome household members, novel food type in cases of possible aversion, similar food type in case of food exclusivity, warming the food particularly if olfaction is an issue, alternatively chilling the food if aromas appear to result in nausea, social interaction while eating, feeding small frequent meals as premature satiety is associated with many disease states. Cats are also particularly sensitive to changes in environmental factors, such as the timing and location of feeding, as well as the food type; smell and “mouth feel” may also play into their willingness to eat.8
Medical Management of Underlying Disease
Whenever possible it is obviously ideal to address the underlying disease condition. However in some chronic diseases, i.e., kidney disease, this is not possible and therefore medical management of complications of chronic disease are ideal. Dehydration and anemia can both potentially play a role in inappetence and therefore should be addressed when applicable.
For both acute and chronic medical conditions, appropriate management of pain is critical to improving appetite. Opioids are perhaps most commonly utilized. Buprenorphine has a significantly longer half-life and may be useful for in home palliation of chronic pain. Butorphanol may also have some visceral analgesic properties. Opioids should be used with caution in patients with ileus. Maropitant may also have some visceral analgesic properties.9
Learned Food Aversion
Care should be taken to select the appropriate patients for appetite enhancement as learned food aversion is thought by most to be prevalent in cats.8 Learned food aversion occurs when the patient associates nausea, pain or other physical manifestations of disease with the act of eating or the sight or scent of food. Even after the underlying illness is resolved, this aversion may remain. Therefore it is critical that cats that are overtly nauseous – drooling, gagging, turning away from food – particularly in hospital or in acute illness are not forced to eat lest food aversion be created.8
If cats are too nauseous or critical to even consider oral feeding, or have not responded to appetite encouragement after 3–5 days, placement of an enteral feeding tube should be considered. Nasoesophageal, esophageal or gastrotomy tube can be chosen depending on the type and duration of feeding desired.2 Esophageal feeding tubes can be a valuable tool for long-term management of CKD patients as food, medications and water can be easily given without stressing the patient. Parenteral feeding should be considered in cats that cannot tolerate enteral feeding. Additionally many clinicians feel that prescription diets (i.e., renal) should not be fed in hospital during a crisis lest an aversion be created to the diet desired for long term management. The best candidates for pharmacological enhancement of appetite are cats leaving the hospital with their acute crisis resolved, and cats with chronic disease in the home environment.
Cats with CKD likely suffer from nausea, vomiting and inappetence as a result of uremia – a buildup of toxins in blood – that affects the chemoreceptor trigger zone in brain. In addition, uremia may have effects on the intestinal tract that lead to further unwillingness to eat. Several antinausea therapies have become recently available. These include maropitant, ondansetron and dolasetron. These drugs work at nausea center in brain as well as in gut and can be given as an injection. Ondansetron has been documented to be helpful in human patients suffering from uremia.10 However recent pharmacokinetic studies in cats have demonstrated that oral bioavailability of ondansetron is poor in cats (~ 35%) and the half-life is very short (approximately 1 hour) making it a q 8 h medication.11 Subcutaneous ondansetron has a slightly longer half-life of 3 hours. In addition to its appetite-stimulating properties, mirtazapine demonstrates antinausea properties as it acts at the 5HT3 receptor similarly to ondansetron and dolasetron.12,13 Limiting gastric acidity with the use of H2 blockers or proton pump inhibitors such as famotidine or omeprazole respectively anecdotally appears to palliate inappetence in some patients, however as previously mentioned both the degree of hyperacidity present in CKD and the efficacy of these medications for management of cats with CKD remains unproven. Recent studies of the effect of omeprazole on the gastric pH in cats indicates that it is superior to famotidine in its ability to inhibit acid production and twice daily dosing is necessary.14
Maropitant is commonly used for acute vomiting. A pharmacokinetic and toxicity study in cats indicated that longer- term usage appears safe.15 A recent study assessed the efficacy of maropitant for management of chronic vomiting
and inappetence associated with feline CKD.16 When given daily for two weeks, maropitant was demonstrated to palliate vomiting associated with chronic kidney disease, however did not appear to significantly improve appetite or result in weight gain in cats with Stage II and III CKD within the timeframe of the study.
APPETITE STIMULANT THERAPY
Cyproheptadine has been used for some time as an appetite stimulant and has anecdotal efficacy in many patients, however its efficacy has never been scientifically evaluated. Twice daily administration is necessary in many cases and this can prove a challenge for owners, particularly long term. Sedation is a common side effect. Mirtazapine has become more commonly used and recent exploration of its pharmacodynamics and pharmacokinetics have provided information for more effective use in cats.17,18 Pharmacodynamic studies have illustrated that it can be a potent appetite stimulant, but higher doses are more commonly associated with side effects (hyperexcitability, vocalization, tremors). Smaller, more frequent doses are recommended. The half-life is short enough that it could be administered daily in normal cats. Renal disease delays clearance and in these patients, every other day administration is recommended.17 Owners should be aware mirtazapine and cyproheptadine cannot not be administered concurrently; cyproheptadine is in fact used as an antidote for serotonin effects of mirtazapine overdose.
A recent placebo-controlled, double-masked crossover clinical trial was performed to evaluate the effects of mirtazapine on body weight, appetite, and vomiting in cats with CKD.13 Mirtazapine is an effective appetite stimulant
in cats with CKD and resulted in significantly increased appetite and weight. Mirtazapine also appears to have antiemetic properties and resulted in significantly decreased vomiting in cats with CKD. This drug could be a useful adjunct to the nutritional management of cats with CKD.