Safety of an amino-acetonitrile derivative (AAD), monepantel, in ewes and their offspring following repeated oral administration

Abstract

AIM: To demonstrate the clinical and reproductive safety in ewes and their offspring of repetitive oral doses of monepantel, an amino-acetonitrile derivative (AAD), when administered at three times the proposed maximum recommended dose (MRD) over an entire reproductive cycle. METHODS: A randomised controlled blinded study design was used. One hundred and twelve primi- or multi-parous ewes and 28 rams were randomly allocated into control and treated groups (n=56 for groups of ewes, n=14 for groups of rams). Two control ewes and two treated ewes were randomly selected to form 28 subgroups. A control or treated ram was then randomly allocated to each subgroup, to form control ram/treated ewe, control ram/control ewe, treated ram/treated ewe, and treated ram/control ewe ‘treatment/mating’ units. Control animals were treated with saline, and treated animals given three times the MRD (11.25 mg/kg) of monepantel. Treatments were administered orally every 5 days during an entire reproductive cycle, including oestrus and mating, gestation, and post-lambing to weaning. Detailed recording at multiple time points were made of veterinary examinations; observations for adverse events; bodyweight measurements; faecal scores; and haematology, clinical chemistry and coagulation variables. Reproductive indices determined included percent pregnant, number of failed embryos, abortion percentage, number of lambs with teratogenic defects, length of gestation, percentage of stillbirths, number of ewes experiencing reproductive problems, lambing percentage, and pre-weaning mortality. Post-mortem examination, including measurement of organ weights, was performed on randomly selected ewes (n=40) and lambs (n=40) at the completion of the study. RESULTS: All ewes treated with monepantel and those in the control group thrived and behaved normally to the end of the study. No treatment-related, toxicologically relevant adverse events, clinical observations or gross post-mortem changes were observed. Furthermore, there were no significant differences in bodyweight or organ weights, and haematological, clinical chemistry or coagulation variables between ewes treated with monepantel and control ewes. No significant differences were observed in any of the reproductive indices measured. No significant clinical differences were noted between lambs born from treated ewes and those from controls. CONCLUSIONS AND CLINICAL RELEVANCE: Repeated oral administration of monepantel at three times the MRD every 5 days over an entire reproductive cycle was not associated with any treatment-related adverse effects on the reproductive performance of ewes nor on the viability of their offspring, and was systemically very well tolerated. This study demonstrated that this population of ewes could tolerate accidental overdoses of up to three times the MRD of monepantel or prolonged repetitive administration of overdoses. Thus, those so treated entering a breeding programme would have normal reproductive indices, mating behaviour, and health, and their lambs would suffer no ill effects.