Toxicological evaluation of long-term intravenous administration of amitraz in horses

With the aim of determining the possible toxicity of amitraz after its prolonged use in horses, six English Thoroughbred horses received intravenous injections of amitraz (0.05, 0.10 or 0.15 mg/kg) weekly for four months, constituting the experimental group. Eight other animals (control group), via the same route following the same drug administration schedule and period of time, received the vehicle, dimethylformamide. At the end of this period, blood was collected from all the animals, and a comparison was made of the means of the values obtained for the various blood analyses: complete hemogram, alkaline phosphatase, gamma-glutamyltransferase, blood urea nitrogen, lactate dehydrogenase, aspartate aminotransferase, creatine phosphokinase, glucose, albumin, total protein, creatinine, Na+ , K+, Cl- and CO2. The results for the biochemical characteristics showed that only the mean value for urea of the animals submitted to treatment with amitraz was significantly different than the mean value obtained for the control group. The analyses of the hematological characteristics showed that no significant differences between groups were observed. Similarly, the measurement of blood electrolyte levels demonstrated that long-term treatment with amitraz did not cause significant changes in the variables analyzed. The results indicate that amitraz, given in the doses employed in this study, did not show signs of inducing toxic effects in vital organs, even after prolonged administration

Efeitos do amitraz e da xilazina sobre algumas características fisiológicas de cavalos / Effect of amitraz and xylazine on some physiological variables of horses

Avaliaram-se os efeitos das injeçöes intravenosa (iv) de amitraz (0,1mg/kg) e xilazina (1mg/kg), em cavalos, sobre a atividade cardíaca, freqüência respiratória, atividade motora intestinal, temperatura retal, sudorese e freqüência de apreensäo de alimentos. O amitraz causou diminuiçäo significativa da atividade cardíaca, da freqüência respiratória e da movimentaçäo intestinal, mas esses efeitos näo foram täo pronunciados quanto os causados pela xilazina. O amitraz causou, também, relaxamento significativo da musculatura lisa retal, e um aparente aumento da sudorese e da freqüência de cavalos flagrados mastigando feno. A temperatura retal näo foi influenciada pelo amitraz. Os resultados indicam que o amitraz, na dose utilizada, näo causou efeitos colaterais severos em cavalos