Capromorelin for CKD Weight Loss: 176-Cat Trial Data

In a 176-cat field trial, cats with chronic kidney disease and at least 5% unintended weight loss gained 5.18% of body weight in 55 days on capromorelin, while the placebo group lost 1.65%. The gap, 0.25 kg, is the difference between a 4.1 kg cat that keeps sliding and one that stops.

What the 176-cat trial measured

The study behind the FDA approval was multicenter, randomized, masked and vehicle-controlled: 118 cats received capromorelin at 2 mg/kg once daily and 58 received the carrier solution, a 2:1 split over 56 days. Mean age was 15.1 years (range 4.4 to 22.1) and mean weight 4.1 kg (1.8 to 6.8). Weight was the primary endpoint, analysed in 112 cats that completed the protocol.

Scored as pass or fail, meaning any change of 0% or better, 83.1% of treated cats counted as successes against 41.5% of controls.

Why CKD cats lose weight years before the diagnosis

Weight loss is not a late complication of kidney disease; it is often the first sign. A 2016 study of cats with CKD (J Vet Intern Med 30:1661) found a median 8.9% weight loss in the 12 months before diagnosis, with growth-curve analysis placing the start of the slide as much as 3 years earlier. At enrollment in the capromorelin trial, 43.2% of cats already had moderate or severe muscle loss and 88.1% had dental disease. Cornell puts CKD prevalence at up to 40% of cats over 10 and 80% over 15, and cats under 4.2 kg (9.3 lb) at diagnosis have significantly shorter survival. The loss is fat and lean mass together, which is why a cat can look merely old while losing 100 g a month.

How capromorelin works, and how it is given

Capromorelin is a ghrelin receptor agonist: it mimics the hunger hormone. It binds receptors in the hypothalamus to drive appetite and in the pituitary to raise growth hormone, which lifts IGF-1 from the liver, and IGF-1 stays elevated while the drug is given. The label dose is 2 mg/kg (0.9 mg/lb) once daily, which for the 20 mg/mL oral solution works out at 0.1 mL/kg, or 0.4 mL for a 4 kg cat. Food is offered about 30 minutes after dosing, and a dose vomited within 15 minutes may be repeated. Dosing after a meal softens the peak: a meal cuts maximum concentration about 55% and total exposure about 43%.

Who the label covers, and who it does not

Trial eligibility was narrow and worth copying: CKD diagnosed at least 30 days earlier, documented unintended loss of 5% or more, and stable treatment for everything else. Most cats were IRIS stage 2 (66.5%), with 11.4% in stage 1, 21.0% in stage 3 and 1.1% in stage 4. The label adds caution for cardiac disease, severe dehydration and liver dysfunction, and has not been evaluated in cats under 5 months or in breeding, pregnant or lactating queens. A dehydrated cat that is vomiting is not a capromorelin case yet; fluids and a diagnosis come first, and the 24 and 48 hour lines still apply.

Side effects, and the four-hour window

Hypersalivation was the only adverse event significantly more common with the drug (P<0.0001); vomiting was also reported, and both were seen more often in males. Any adverse event was recorded in 81.4% of treated cats and 70.7% of controls, a difference that was not significant, because old cats with CKD generate background noise. The effect that changes how you dose is cardiovascular: heart rate and blood pressure dip transiently for up to 4 hours after a dose. The 6-month safety study in healthy cats at 1x, 3x and 5x the label dose produced weight gain in every treated group; one cat at 5x was euthanized on day 50 with diabetic ketoacidosis, and higher MCV, triglycerides and soft feces were also reported more often in treated cats.

Capromorelin or mirtazapine

Both are FDA-approved for weight loss in cats and they are not interchangeable. Mirtazapine is a transdermal ointment, 2 mg per cat once daily as a 3.8 cm ribbon on the inner ear, labelled for 14 days; a crossover trial in 9 and 10 CKD cats found median gains of 0.22 kg and 0.26 kg over 3 weeks given every other day.

Four questions sort them. Is the cat still eating but losing, or genuinely refusing food? Can you get liquid into the mouth, or is the ear the only route the household can manage? Is there a murmur, an arrhythmia or dehydration, all of which argue for a cardiac-aware plan? And do you need months of treatment rather than a two-week bridge?

Cost per month, and what 0.25 kg buys

Retail for the 15 mL bottle runs $53.10 to $57.57 in US pharmacies. At 0.1 mL/kg daily the bottle's life depends on the cat:

• 3 kg cat: 0.3 mL a day, 50 days per bottle, about $32 to $35 a month.
• 4 kg cat: 0.4 mL a day, 37 days per bottle, about $43 to $46 a month.
• 5 kg cat: 0.5 mL a day, 30 days per bottle, about $53 to $58 a month.

A 5 g tube of Mirataz at roughly $53 holds 50 daily doses of 0.1 g, so the two land in the same cost band and price rarely decides between them.

Monitoring: the day-15 weight and the stop rules

The trial's first significant separation came at day 15, +3.26%, about 130 g for a 4 kg cat. Weigh on the same scale at the same time of day every 2 weeks and log body condition and muscle score beside the number, because a cat can gain 200 g of fluid and still lose muscle; a weight trend chart makes the slope visible. Bloodwork follows the usual CKD cycle of creatinine, SDMA, phosphorus, potassium, UPC and blood pressure, with the first recheck 4 to 6 weeks after starting, as laid out in this CKD follow-up plan. Escalate if vomiting becomes daily, if salivation turns every dose into a fight, or if weight is still falling at day 30; then dental pain, hyperthyroidism or intestinal disease is more likely than kidney-related inappetence.

What the drug does not do

No trial has shown that capromorelin slows CKD progression or extends survival; the endpoint was weight, and 55 days is short. It does not replace phosphorus control, potassium supplementation, hydration, blood pressure management or diet, so the 0.3 to 0.6% phosphorus band still governs the bowl. Nor does it guarantee that the new weight is muscle. Treat it as one lever among five, prescribed and monitored by a vet looking at the whole cat.

This article does not replace a veterinary diagnosis. Capromorelin and mirtazapine are prescription drugs; whether to use one, and how much, depends on the individual cat's kidney stage, heart, hydration and other medication.

Terms mentioned in this article

CKDSDMAUPC

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