Fosfatriclaben: Effective dose determination and comparative efficacy assessment with closantel, triclabendazole+ivermectin, triclabendazole+albendazole in artificially infected cattle.

Two controlled efficacy studies were conducted to determine the effective dose of fosfatriclaben (FTCB) and compare its fasciolicidal efficacy with that of three commercial products against eggs and adult stages of Fasciola hepatica in artificially infected cattle. In study 1, 20 trematode-free Holstein Friesian steers were infected on day 0 with 500 F. hepatica metacercariae. Ten weeks after infection and the steers were confirmed to be positive for trematode eggs through a modified sedimentation method. On day 75, they were divided into five groups of four animals each for treatment. Group 1 (G1) served as the untreated control; G2, G3, and G4 received FTCB at 4, 6, and 8 mg/kg/intramuscularly (IM), respectively. G5 received a combined treatment of triclabendazole (TCBZ) (12 mg/kg IM + ivermectin (0.2 mg/kg IM). Individual faecal analyses were performed on days -8, 0, 70, 75, and 105 to evaluate the reduction in trematode eggs. Four weeks after treatment, the steers were humanely slaughtered to harvest the livers and remove the parasites present in the bile ducts. Efficacy was evaluated by the reduction in fecal egg counts or in number of adult parasites, compared to the untreated control. The effective FTCB dose was 6 mg/kg. Once the effective dose was determined, study 2 was conducted on another 20 steers infected with 500 F. hepatica metacercariae, to compare the effectiveness of FTCB with three commercials fasciolicides. All procedures were performed as described in study 1, and treatments were as follows: Group 1 (G1), closantel (5 mg/kg subcutaneously (SC)); G2, TCBZ (12 mg/kg IM) + ivermectin (0.2 mg/kg IM); G3, FTCB (6 mg/kg IM); G4, triclabendazole (12 mg/kg) + albendazole (5 mg/kg/PO (orally); and G5 served as an untreated control. The results indicated that all tested compounds were highly effective in the reduction of faecal egg excretion (99.7-100%) and adult parasites (98.9-100%), except closantel, which exhibited low efficacy (74.4%) when tested against adult trematodes. We concluded that the effective dose of FTCB for cattle was 6 mg/kg IM, which is half the recommended clinical dose of the commercial combination of TCBZ and ivermectin. The fasciolicidal efficacy of FTCB was like the other three flukicides in reducing adult F. hepatica and Fasciola eggs; however, closantel was not sufficiently efficient against adult flukes.