Morantel (+)-tartrate salt

Observations of erratic anthelmintic activity of fenbendazole against known standardised thiabendazole-resistant strains of Haemonchus contortus and Trichostrongylus colubriformis in sheep were investigated. Fenbendazole at a dose rate of 10 mg/kg body weight was administered by oral, intra-ruminal or intra-abomasal routes, and was most effective against both resistant strains following intra-ruminal administration. In addition thiabendazole, oxibendazole, fenbendazole, parbendazole and mebendazole plus two unrelated compounds, levamisole and morantel tartrate, were used at one and a half times their suggested or recommended therapeutic dose rate against thiabendazole-resistant strains of H contortus and T colubriformis in sheep; each drug being administered by the intra-ruminal or intra-abomasal routes. Fenbendazole was more effective against both strains following intra-ruminal administration. Parbendazole was more effective against the resistant strain of T colubriformis following intra-ruminal administration. At the dose rate chosen for the other benzimidazoles used against these resistant strains, there was no difference in anthelmintic efficacy due to route of administration. Levamisole was highly effective against both resistant strains, irrespective of the route of administration.

Treatments with mebendazole, cambendazole or febantel were ineffective in reducing the faecal egg count of a group of 40 horses infected with small strongyle species. Evidence was also obtained that this apparent resistance extended to fenbendazole. In horses dosed with morantel tartrate egg counts were reduced to zero by 7 days after treatment. The development of resistance is discussed in relation to previous treatment of the horses and the mode of action of febantel.

Strains of Trichostrongylus colubriformis (designated PF4) and Ostertagia sp (O circumcincta/O trifurcata, designated PF5), with varying degrees of resistance to levamisole, morantel tartrate and thiabendazole were isolated into pure culture. Detailed dose response studies showed that both T colubriformis and Ostertagia sp were highly resistant to levamisole and morantel with low level resistance to thiabendazole. The effective dose required to remove 80 per cent worm burdens (ED80) was calculated for each anthelmintic. For T colubriformis the ED80 for levamisole and thiabendazole were 12.6 and 40.1 mg/kg respectively. For Ostertagia sp, the ED80 for levamisole, thiabendazole and morantel were 20.4, 45.2 and 35.8 mg/kg respectively. The implications of these results are discussed with reference to alternative means of chemical control.