Safety of a topically applied spot-on formulation of metaflumizone plus amitraz for flea and tick control in dogs

Four laboratory studies were conducted in Beagle dogs to evaluate the safety of a novel ectoparasiticide combination of metaflumizone plus amitraz (ProMeris®/ProMeris Duo® for Dogs, Fort Dodge Animal Health, Overland Park, KS) when applied according to the recommended dosage of ≥20 mg metaflumizone kg−1 plus ≥20 mg amitraz kg−1, at exaggerated and repeated dosages, and if accidentally orally ingested. Parameters evaluated included body weight, food consumption, clinical, physical and neurological examinations, clinical pathology and gross and microscopic pathology. Exaggerated and repeated topical treatment with metaflumizone plus amitraz administered at 1×, 3× and 5× the recommended dose had no effect on clinical findings, heart rates, body weight, food consumption, physical/neurological examinations, macroscopic and microscopic pathology. Very slight, transient, clinically insignificant increases in serum urea nitrogen were noted in some dogs treated at all dose rates tested. This effect was not persistent, was not dose-responsive, nor aggravated by repeated applications and was not associated with a corresponding increase in creatinine or renal pathology. Therefore, these increases in urea nitrogen were suspected to be of non-renal origin and were not considered toxicologically significant. Exaggerated doses (3× and 5×) caused very mild, transient hyperglycemia, most notably in some adult females. Transient and inconsistently noted mild increases in leukocytes, neutrophils and monocytes were observed in some 3× and 5× treated dogs at some intervals. None of the effects noted were aggravated by repeated administration. When 10% of the recommended topical dose was orally administered to mimic exposure due to licking the application, avoidance behaviors including spitting, head shaking, and salivation were noted immediately in all animals. Consequently, voluntary oral ingestion is considered unlikely. Transient decreased activity, slightly reduced body temperature and pale oral mucous membranes were noted in some animals beginning 1–2 h posttreatment. Ataxia, resolving within 4 h posttreatment, was noted in one female. Oral administration had no effect on clinical pathology. Results from these four studies indicate repeated use of metaflumizone plus amitraz causes no adverse health effects when used as recommended in dogs as young as 8 weeks of age.