Regulation and Pharmaceutical Intervention of Appetite in South American Camelids

Abstract

Inappetence is a common clinical problem in hospitalized South American Camelids (camelids), associated with stress or secondary to underlying disease processes. Potential consequences of prolonged inappetence in camelids include weight loss, ketosis, or hepatic lipidosis. Development of an increase in metabolic demand in disease has also been well recognized in human and veterinary medicine. In humans with critical illness, malnourishment has been associated with a poor outcome. In veterinary patients, provision of adequate nutritional support is positively associated with hospital discharge. Options for providing nutritional support to camelids are limited and clinically challenging. Forced enteral feeding is stressful and may potentiate cortisol-induced lipolysis. Intravenous (IV) or parenteral nutrition administration results in more frequent metabolic complications in alpacas compared to other veterinary species and requires frequent monitoring. Increasing voluntary feed intake is often unsuccessful as it relies on increasing feed palatability and decreasing environmental stress. While some pharmacological appetite stimulants have been used clinically in camelids, none have been critically evaluated. Mirtazapine is a noradrenergic and specific serotonergic antidepressant used in dogs and cats for appetite stimulation and weight gain. The pharmacokinetics of mirtazapine show species-specific differences but have not been investigated in alpacas. In fact, pharmacokinetic studies in alpacas are sparsely reported in the literature, and the effect of site of sample collection on plasma concentrations of a drug, which is known to differ in other species, has not been investigated in pharmacological studies of camelids. The aim of this study was to determine the pharmacokinetics of a single dose of orally administered mirtazapine in healthy adult alpacas and to compare concentrations of mirtazapine at two venous sample sites after oral administration.