Efecto de la Aplicación Tópica de una Solución Comercial de Amitraz sobre el Cronotropismo y Dromotropismo Cardiacos en Ratas Anestesiadas y Perros Conscientes

amitraz is a diamidine molecule widely used as an ectoparasiticide in veterinary medicine. although amitraz is prescribed as a topical treatment, its toxicity has been reported in oral and intravenous administration. this investigation assessed the potential chronotropic and dromotropic effects of topical amitraz (12% v/v; 4ml/l) in anesthetized rats and conscious dogs. sixteen rats and twelve dogs were used. before treatment, body surface was moistened with water and all animals were subjected to a baseline electrocardiogram (ecg). subsequently, amitraz was applied to rats (n=16) as an immersion bath for 2 min, or as a spray application to dogs (n=12), respectively. two consecutive ecgs were recorded at 30 min interval for 1 h. the heart rate (hr) and the p-r intervals were calculated to estimate chronotropism and dromotropism, respectively. the hr of rats was reduced (control: 265.7±12.1 beats/min vs amitraz: 234.4±13.8 beats/min) at 30 min after amitraz application, reaching a significant (p<0,05) value at 60 min (225.0±13.6 beats/min). the p-r interval was significantly (p<0.05) prolonged at 30 min (control: 54.3±2.0 msec vs amitraz: 67.9±2.4 msec) and 60 min (72.1±2.8 msec), respectively. in contrast, no significant changes in hr and p-r interval were found in dogs treated with amitraz. the negative chronotropic and dromotropic effects observed in rats may reflect the activation of pre-synaptic a2-adrenoceptors in the central nervous system and a reduction in the sympathetic outflow, without excluding a potential parasympatomimetic effect. the lack of these effects in dogs might be related either to reduced skin absorption or to a potential autonomic regulatory reflex in conscious dogs. the therapeutic dose of amitraz used herein did not modify the ecg in apparently healthy dogs. further experiments are required to establish the effects of higher topical doses in dogs suffering from skin diseases related to mites or ticks infestations.