Coccidiosis is a detrimental disease caused by development and reproduction of multiple species of the Eimeria protozoa and affects numerous species. In the commercial broiler industry, Eimeria protozoan parasitizing on the intestinal epithelium of chicken resulted in significant increase in mortality and morbidity, and led to considerable impairment of growth and feed utilization, which is capable of inflicting devastating economic losses to poultry operations. It is estimated that the substantial economic burden caused by avian coccidiosis was more than US$3 billion annually to the industry worldwide [1, 2]. Due to the defects of vaccines, commercial synthetic anticoccidial drugs have been the main strategy of the control of coccidiosis since the late 1940s [3]. However, more and more clinical studies showed that the widespread resistances to commercial anticoccidial drugs have emerged in coccidian parasites for continuous use and misuse of anticoccidial drugs [2, 4]. Consequently, the resulting letdown of treatment promotes a constant demand for innovative products with safe and efficient. Triazines are benzene-aceto-nitrile compounds including diclazuril, toltrazuril, ponazuril and clazuril, which have been used globally in the interception and therapy of protozoal diseases, most commonly in coccidiosis of veterinary interest since 1980s [5]. However, the widely use of triazine coccidiostats for their remarkable clinical effects have generated resistance to the genus Eimeria in recent years [5, 6]. Fortunately, no cross-resistance was observed in triazine coccidiostats [5].
Ethanamizuril (Fig. 1), a novel triazine coccidiostat, namely (N-(4-(4-(3,5-dioxo-4,5-dihydro-1,2,4-triazin-2-(3H)-yl)-2-methylphenoxy) phenyl)acetamide, has been independently established by the Shanghai Veterinary Research Institute of the Chinese Academy of Agricultural Sciences in recent years and exert wide application prospective in future [5, 7]. In China Patent No. ZL 2013105527952 and Japan Patent No. 6106798, the chemical synthesisit of ethanamizuril and the chemical structure, have been published [8]. Ethanamizuril has displayed excellent effectiveness against Eimeria protozoa such as Eimeria tenella, Eimeria. necatrix, Eimeria. acervulina, and Eimeria. maxima in broiler chickens at a dosage of 10 mg/kg in the feed or 10 mg/l in the drinking water [7, 8]. At the recommended dose, ethanamizuril could prominently improve feed conversion ratios and live weight, reduce oocyst excretion, mortality and lesions in broilers. ACIs (anticoccidia indexes) of ethanamizuril reached 185 ~ 190. Furthermore, the preclinical pharmacodynamic studies demonstrated ethanamizuril did not cause cross-resistance with diclazuril or toltrazuril resistant Eimeria. tenella in broilers.
Because of the diverse toxicities, the use of some coccidiostats, such as arprinocid, roxarsone and arsanilic acid has been forbidden in poultry industry [9, 10]. Up to now, a series of studies have been conducted to evaluate the safety of diclazuril and toltrazuril for use as coccidiostats. Increase of liver weight and swelling of the centrilobular hepatocytes were seen in diclazuril treated mice and rats [11, 12, 13]. The slight effects on haematological parameters, disturbances of the liver function and decreased on the weight gain and the daily feed intake were observed in toltrazuril treated rats [11, 12, 14]. In addition, in two teratogenicity studies, teratogenicity and embryotoxicity were observed at the toltrazuril highest dose in rats [14, 15]. With high anticoccidial effectiveness, ethanamizuril would be used widely in poultry industry in future. To the best of our knowledge, although a series of toxicity evaluation of ethanamizuril has been carried out in rats and mice, the toxicity evaluation in beagle dogs has not been reported [11, 12, 15]. This is unfavourable for understanding the safety and clinical use of ethanamizuril. In order to understand the toxicity profile of ethanamizuril, we conducted the 90-day subchronic toxicities of ethanamizuril in beagle dogs in accordance with the guidelines of veterinary safety evaluation.