A large-scale clinical field study to evaluate the efficacy and safety of an oral formulation of the amino-acetonitrile derivative ( AAD ), monepantel , in sheep in New Zealand.

AIM

To evaluate the efficacy and safety of an oral formulation of the novel anthelmintic, monepantel (AAD 1566), in sheep, in comparison with some other anthelmintics currently registered in New Zealand.

METHODS

A study was conducted on 18 farms located throughout the North and South Islands of New Zealand. On each farm, sheep naturally infected with the target nematodes were randomly assigned to groups, which were then treated with either monepantel, at a minimum dose rate of 2.5 mg/kg, or one of five other anthelmintics encompassing the range of single-entity and combination formulations that are commercially available in New Zealand, or left untreated as controls. Faecal samples were collected from all sheep pre-treatment (1-3 weeks before treatment), at the time of treatment, and approximately 1, 2 and 3 weeks after treatment (Days 7, 14 and 21). Faecal nematode egg counts (FEC) were measured in all samples, and the efficacy of treatments, as indicated by reductions in FEC, calculated. All sheep were inspected at least daily, to check for any adverse effects of treatment.

RESULTS

On all 18 farms, on Days 7, 14 and 21 (54 test points), the efficacy of the monepantel solution was >95%. At Days 7 and 14 post-treatment, efficacies>99% were recorded in 15 flocks. At Day 21 post-treatment, efficacies>98% were recorded in 13 flocks. Monepantel was as effective, or more effective, than the registered anthelmintics with which it was compared. Moreover, it was effective against strains of nematodes resistant to one or more of the currently available broad-spectrum anthelmintics. The monepantel solution used in this study was well tolerated by the sheep, and no adverse events could be attributed to its use.

CONCLUSIONS AND CLINICAL RELEVANCE

When administered as an oral formulation under field conditions, at a minimum dose rate of 2.5 mg/kg, monepantel appeared to be highly effective against all the major genera of gastrointestinal nematodes of sheep, including Haemonchus, Teladorsagia (=Ostertagia), Trichostrongylus, Cooperia, Nematodirus, Chabertia and Oesophagostomum. This included strains resistant to the currently available broad-spectrum anthelmintics. Monepantel is the first compound from the recently discovered amino-acetonitrile derivative (AAD) class of anthelmintics to be developed for use in sheep.