Emulsão lipídica no tratamento de coelhos Nova Zelândia intoxicados pela ivermectina

Abstract

Accidental poisonings by ivermectin, a highly lipophilic drug, are common in veterinary medicine, but still no antidote is known. The use of intravenous lipid emulsions (ILE) in toxicosis caused by lipophilic agents is becoming more common each day. Although there are reports of the use of this therapy in ivermectin poisoning, to the author's knowledge there are no experimental controlled studies to assess the effect of this treatment. The aim of this study was to observe the changes caused by ivermectin toxicity in New Zealand rabbits, the effect of ILE in these animals, and to evaluate the safety of this therapy. Twenty four New Zealand rabbits where randomly divided into four groups (n = 6). At time zero ivermectin was given through nasogastric tube at a dose of 8ml/kg (80mg/kg) to three groups, while the fourth group received the same volume of saline. Of the three groups exposed to ivermectin, the first did not received further treatment, while, three hours after this drug was administrated, the second received lactated Ringer intravenous infusion (initial bolus of 2ml/kg followed by continuous infusion at the rate of 0.25ml/kg/min for 60 minutes) and the third received 20% lipid emulsion at that same rate. The fourth group only received lipid emulsion. All animals underwent clinical and neurological evaluation at time zero, one and a half, three, four and six hours, and blood sampling for hematological and biochemical analysis at time zero, three, four and six hours. Hematological analysis consisted of complete blood count, while serum biochemistry consisted of measurement of urea, creatinine, triglycerides, cholesterol, glucose, albumin and total protein concentrations, and alanine aminotransferase, aspartate aminotransferase, gamma glutamyl transferase and alkaline phosphatase enzyme activity. Animals were euthanized six hours after ivermectin or saline was administrated, after which kidney, liver, brain and fat samples were immediately collected for toxicological analysis. This was based on quantification of ivermectin, extracted by the modified method of QuEChERS and detected by high-performance liquid chromatography followed by spectrometric mass. For histopathologic analysis, kidney, liver, brain and spleen samples were also obtained. All animals exposed to ivermectin manifested clinical changes consistent with toxicosis, such as bradypnea, hypothermia and, most commonly, neurological alterations. Among the neurological changes, altered posture, mentation, cranial nerves, gait, postural and myotatic reflexes, muscle tone and breathing patterns, as well as the presence of tremors and impaired ability to return to the starting position when placed in the supine dorsal recumbent position were observed. A few animals showed manifestations compatible with lower motor neuron lesion, which are not frequently found in this type of poisoning. Ivermectin caused intense increase in serum glucose and triglyceride levels, and increased urea and creatinine, but these remained within the reference range. With these findings, associated with the pathological observations in the organs sampled, it was concluded that ivermectin poisoning caused no significant liver or kidney damage, as well as no liver, kidney, brain and spleen histopathologic change. Toxicological analysis showed greater ivermectin concentration in adipose tissue and liver, followed by kidney and, finally, brain. The animals that received ILE infusion showed no significant clinical improvement or change in ivermectin concentration. It is possible, however, that if the treatment was performed earlier or monitoring was maintained for a longer period, an effect of the ILE on these parameters would have been observed. Lipid emulsion infusion was considered clinically and histologically safe, despite causing a significant increase in serum triglycerides and cholesterol