Evaluation of the safety in dogs of long-term, daily oral administration of capromorelin, a novel drug for stimulation of appetite

Insights on discovery, efficacy, safety and clinical applications of ghrelin receptor agonist capromorelin in veterinary medicine

Growth hormone and insulin like growth factor-1 plays an important role in the regulation of body composition and metabolism. Growth Hormone is released from the pituitary through a specific G-protein coupled receptor (GPCR) called growth hormone secretagogue receptor 1a expressed in the hypothalamus. Ghrelin is a peptide hormone released from the cells in the stomach, which stimulates appetite and food intake in mammals, regulates gut motility, gastric acid secretion, taste sensation, circadian rhythm, learning and memory, oxidative stress, autophagy, glucose metabolism etc. When the release of the endogenous ligand GHSR-1a, i.e., ghrelin is malfunctioned or stopped, external substitutes are administrated to induce the stimulation of growth hormone and appetite. A class of compound known as ghrelin receptor agonists are developed as an external substitute of ghrelin for regulation and stimulation of growth hormone in frailty, for body weight gain, muscle mass gain, prevention of cachexia and for the treatment of chronic fatigue syndromes. Capromorelin [Entyce™ (Aratana Therapeutics, Leawood, KS, USA)] is the only FDA (Food and Drug Administration) approved (May 2016) drug used for stimulating appetite in dogs and was marketed in the fall of 2017. In 2020, USFDA approved Capromorelin [Elura™ (Elanco US Inc.)] for the management of weight loss in chronic kidney disease of cats. This article reviews the discovery of the ghrelin receptor agonist capromorelin, its efficacy, safety, clinical applications and aims to delineate its further scope of use in veterinary practice.

Detection of capromorelin in urine following oral and dermal routes of administration

Capromorelin is a growth hormone secretagogue. Despite promising results to alleviate muscle-wasting in the elderly, it has not advanced further in human development. Subsequent studies demonstrated capromorelin's ability to increase food intake in animals, leading to approval in the United States and Europe as an appetite stimulant for cats (Elura) and dogs (Entyce). Capromorelin is prohibited in sports due to its ability to stimulate growth hormone production and enhance performance. However, given that its veterinary preparation is formulated as a highly concentrated solution (20 or 30 mg/mL) delivered orally, incidental ingestion or dermal absorption may result in an adverse analytical finding (AAF) by way of direct exposure during oral administration to a pet. An administration study was conducted by either oral or transdermal application of capromorelin solution to mimic the scenario of inadvertent exposure to the drug. Ingestion of 30 μg of capromorelin orally (equivalent to 1 μL of Entyce) resulted in detectable amounts of capromorelin in urine for up to 48 h after administration with a maximum urinary concentration of 7 ng/mL. Importantly, when applied directly to the skin on the hands in larger quantities mimicking a pet administration exposure scenario (30 mg or 1 mL of Entyce), capromorelin was also detected reaching a maximum urinary concentration of 0.7 ng/mL. Athletes and testing authorities should be aware of the risk of an AAF arising due to incidental exposure to veterinary preparations of capromorelin. To our knowledge, before 2022, no positive test for capromorelin had ever been reported.

The effect of capromorelin on glycemic control in healthy dogs

Capromorelin is a ghrelin-receptor agonist widely used as an appetite stimulant in dogs. Capromorelin disrupts glucose homeostasis in cats but information regarding its effects on canine glucose homeostasis is lacking. The study objective was to evaluate the effect of capromorelin on glucose homeostatic mechanisms in healthy dogs. Eight clinically healthy client-owned adult dogs were enrolled in this prospective, cross-over, placebo-controlled study. Dogs were randomized to receive capromorelin (Entyce, 3 mg/kg) or placebo, q24h for 3 d. A wk later, treatments were crossed over. Interstitial glucose (IG) concentrations were measured using a flash glucose monitoring system throughout. On d 1 of each treatment, blood glucose (BG), insulin, glucagon, glucose-dependent insulinotropic peptide (GIP), and glucagon-like peptide-1 (GLP-1) concentrations were measured before drug administration, then before and 30-120 min after feeding a glucose-rich diet (Ensure Plus, 21 kcal/kg). Data were analyzed as a 2-period crossover design using generalized least squares estimation. Capromorelin administration increased mean 48 h IG by10% and mean BG by 20% at 90 and 120 min post-prandially (P < 0.0001). Post-prandially, there was a time-by-treatment effect for insulin (P = 0.03) and GIP (P = 0.0002) because capromorelin doubled geometric mean insulin concentrations at 120 min and increased geometric mean GIP concentrations more rapidly than after placebo. There were no differences in glucagon or GLP-1 concentrations between treatment groups. The increase in post-prandial blood glucose was not the result of overt suppression of incretin hormone secretion. There was also no suppressive effect of capromorelin on insulin.

Comparison of Effects of Capromorelin and Mirtazapine on Appetite in New Zealand White Rabbits (Oryctolagus cuniculus)

Inappetence is a welfare concern in rabbits (Oryctolagus cuniculus), as it can lead to potentially fatal gastrointestinal stasis. In other species, inappetence is commonly treated with appetite stimulants; however, few published studies have evaluated the efficacy of appetite stimulants in rabbits. We performed 2 studies to evaluate the effects of capromorelin and mirtazapine on appetite in New Zealand White (NZW) rabbits. In the first study, healthy rabbits ( n = 9) were evaluated using a randomized crossover design and 9 treatments: capromorelin 4 mg/kg oral (PO) once a day (SID), capromorelin 8 mg/kg PO SID, saline control PO SID, capromorelin 4 mg/kg PO twice a day (BID), capromorelin 8 mg/kg PO BID, saline control PO BID, mirtazapine 0.5 mg/kg transdermal (TD) SID, mirtazapine 1 mg/kg TD SID, and saline control TD SID for 3 d with a 1-wk washout period between treatments. Treatment efficacy was assessed by measuring daily feed intake and fecal output and by weighing rabbits twice a week. Overall, feed intake and fecal output were higher for all treatments as compared with controls, except for fecal output in the capromorelin 4 mg/kg and 8 mg/kg PO SID groups. Feed intake and fecal output were significantly higher with mirtazapine as compared with capromorelin. Body weight and erythema/petechia of the pinnae were greater in the mirtazapine 1 mg/kg TD SID group than in the control group. A second study evaluated rabbits that had undergone surgery (castration, n = 7) and then received one of 3 treatments: capromorelin 8 mg/kg PO BID, mirtazapine 1 mg/kg TD SID, or saline PO BID for 3 d postoperatively. Feed intake and fecal output in the postoperative mirtazapine group were not significantly different from those of the capromorelin and control groups. Due to its superior efficacy as compared with capromorelin in healthy NZW rabbits, we recommend considering mirtazapine as a treatment for inappetence in NZW rabbits.

Anorexia and the Cancer Patient

Appetite influences perceived quality of life for a dog or cat with cancer. Inappetence often is multifactorial, complicating treatment. Cancer-related anorexia/cachexia syndrome is a metabolic, paraneoplastic syndrome characterized by decreased food intake, involuntary weight loss, and loss of fat and muscle. If weight loss/cachexia has an impact on canine and feline cancer patients as in humans, management may improve survival times and quality of life. The challenge is having effective, proved therapies available for clinical use. Recent Food and Drug Administration approvals for appetite stimulation have renewed interest and discussion and has the potential to alter the course of case management.

Perspectives on Feeding and Nutrition

Many palliative care patients have reduced oral intake during their illness. Managing inadequate intake through appetite stimulation and/or artificial hydration and nutrition poses many clinical, ethical, and logistical dilemmas. This article aids the health care team in making appropriate recommendations regarding assisted nutrition and hydration for palliative care and terminal patients. It provides a decision-making framework, including an ethical approach to determining appropriate use of assisted feeding and hydration methods in pets at the end of life. It also summarizes various clinical and logistical approaches to treating decreased food/water consumption, including potential benefits and burdens, should intervention be deemed appropriate.

Capromorelin: a ghrelin receptor agonist and novel therapy for stimulation of appetite in dogs

Ghrelin is a hormone, secreted from cells in the stomach, which is important in the regulation of appetite and food intake in mammals. It exerts its action by binding to a specific G-protein-coupled receptor, the growth hormone secretagogue receptor 1a (GHS-R1a) which is found in areas of the brain associated with the regulation of food intake. Ghrelin causes a release of growth hormone (GH) through binding to GHS-R1a in the hypothalamus and pituitary gland. A class of compounds known as growth hormone secretagogues, or ghrelin receptor agonists, were developed for therapeutic use in humans for the stimulation of GH in the frail elderly, and have subsequently been studied for their effects on increasing appetite and food intake, increasing body weight, building lean muscle mass, and treating cachexia. Subsequent research has shown that ghrelin has anti-inflammatory and immunomodulatory effects. This article reviews the basic physiology of ghrelin and the ghrelin receptor agonists, including the available evidence of these effects in vitro and in vivo in rodent models, humans, dogs and cats. One of these compounds, capromorelin, has been FDA-approved for the stimulation of appetite in dogs (ENTYCE ®). The data available on the safety and effectiveness of capromorelin is reviewed, along with a discussion of the potential clinical applications for ghrelin receptor agonists in both human and veterinary medicine.

A Prospective, Randomized, Masked, Placebo-Controlled Clinical Study of Capromorelin in Dogs with Reduced Appetite

BACKGROUND

Reduced appetite is a common clinical sign in dogs. This study evaluated the effectiveness and safety of capromorelin oral solution, (ENTYCE^® , Aratana Therapeutics, Leawood, KS) a new drug that is a ghrelin receptor agonist, for stimulation of appetite in dogs with reduced appetite.

HYPOTHESIS/OBJECTIVES

Capromorelin will increase appetite, as measured by the owner's evaluation, over 4 days. An additional objective was to evaluate the safety of capromorelin at the labeled dose.

ANIMALS

A total of 244 client-owned dogs reported by owners to be inappetent for at least 2 days were enrolled, with 177 cases in the effectiveness analysis.

METHODS

In this prospective, randomized, masked, placebo-controlled study, dogs were treated daily with capromorelin (3 mg/kg) oral solution (n = 121) or placebo oral solution (n = 56). Owners completed an evaluation of appetite at days 0 and 3 ± 1. Success was defined as improvement in appetite at day 3. Safety was evaluated by physical examination, clinical pathology, and monitoring adverse events and owner observations.

RESULTS

Capromorelin treatment improved appetite compared to placebo (68.6% and 44.6% treatment successes with 95% CI 59.7, 76.3 and 32.2, 57.8, respectively, P = .008). Mean body weight in capromorelin-treated dogs increased compared to placebo-treated dogs (1.8% with 95% CI 1.3, 2.3, and 0.1% with 95% CI 0.9, 1.1, respectively, P < .001). Adverse reactions occurring in >5% of either group were diarrhea and vomiting.

CONCLUSIONS AND CLINICAL IMPORTANCE

Capromorelin oral solution is an effective treatment for stimulation of appetite in dogs and represents the first ghrelin receptor agonist shown to be effective for this indication.

Capromorelin oral solution (ENTYCE®) increases food consumption and body weight when administered for 4 consecutive days to healthy adult Beagle dogs in a randomized, masked, placebo controlled study

Background

Dogs can suffer from inappetence caused by a variety of medical conditions. This may present as anorexia (complete loss of appetite), hyporexia (decreased appetite) or dysrexia (change in food preferences). A drug with a new mechanism of action, capromorelin, has potential to stimulate appetite in dogs. Capromorelin is a ghrelin receptor agonist, which mimics the action of endogenous ghrelin. It is a member of the growth hormone secretagogue (GHS) class of drugs. Capromorelin oral solution (ENTYCE®) was tested in healthy adult male and female Beagle dogs (n = 6 males and 6 females per group) for its effect on food consumption and body weight. A randomized, masked, placebo controlled study was conducted to measure the effects of a daily 3 mg/kg oral dose given over 4 days. Dogs were observed for clinical signs, physical examinations were completed prior to and at the end of treatment, and blood was drawn before and after treatment for evaluation of serum chemistry and hematology parameters.

Results

Capromorelin was well-tolerated, with no abnormalities seen on physical examination or clinical pathology. Some dogs showed increased salivation. Capromorelin treated dogs had increased mean (±SD) food consumption compared to placebo treated dogs (60.55 ± 39.87% versus -11.15 ± 14.23% respectively, P < 0.001). Treated dogs also had increased mean body weights compared to placebo treated dogs (5.96 ± 1.76% versus 0.053 ± 1.14% respectively, P < 0.001).

Conclusions

This study supports the effectiveness of capromorelin oral solution as an appetite stimulant in dogs. Treatment with the oral solution resulted in dramatic increases in appetite, as measured by food consumption, of over 60% compared to placebo. The drug was well tolerated. Capromorelin is the first ghrelin receptor agonist developed for appetite stimulation in any species, and represents a novel mechanism of action for this clinical use.