Determination of the maximum tolerated dose and the safety index of an experimental fasciolicide in cattle.

The aim of the present study was to determine the maximum tolerated dose (MTD) and the safety index (SI) of 5-chloro-2-methylthio-6-(1-napthyloxy)1H-benzimidazole, called compound alpha, in cattle. In addition, to search for possible adverse effects after treatment, the measurement of some biochemical, haematological and physiological parameters were also analysed. Eighteen crossbred heifers were divided into six groups of three animals each. Groups 1-5 received a single oral dose of 12, 36, 60, 120 and 180 mg/kg of body weight (bw) of compound alpha. Group 6 served as an untreated control. To determine the biochemical, haematological and enzymatic parameters, sera and blood samples were individually taken at 0, 4, 8, 16, 32, 128, and 720 h after treatment. Physiological parameters such as rectal temperature, heart rate (HR), respiration rate (RR) and ruminal motility were measured at the time intervals mentioned above. Estimation of the MTD and SI was obtained by using the formula reported by the Food and Drug Administration (FDA), the results showing an MTD of 180 mg/kg/bw and an SI of 15 times the recommended clinical dose. Some statistical differences were observed in a few of the biochemical, haematological and enzymatic parameters, the adverse effects being not highly representative. Alterations on HR and RR were statistically different (P<0.05) only in heifers treated with 180 mg.