Background: A formulation containing 39.6% spinetoram resulted in a higher than anticipated number of reports of alopecia at the site of application in the first months following commercial product launch.
Hypothesis/objectives: To determine the cause of the alopecia using histopathology, including assessment for inflammation, follicular findings of physical trauma (plucking/pulling behaviour) and changes in follicular cycling.
Animals: Twenty-four flea-free, male and female adult domestic short hair cats within a private research colony.
Methods: Cats were treated with a single application of 39.6% spinetoram on day 0; personnel were not blinded. Observations of the skin and hair coat began immediately and were repeated at 30 min and 1, 2, 3, 4, 6, 8 and 12 h post-application and then on subsequent days at the same time as initial dosing and at 2, 4, 6, 8 and 12 h after that time, until day 5. If hair thinning or loss was observed, a skin biopsy sample was collected. Two cats not exhibiting abnormalities were biopsied on day 6.
Results: Thirty-eight per cent of cats (nine of 24) developed hair thinning and alopecia of sufficient severity within 78 h post-application of the product to warrant skin biopsy. Abnormalities in the skin were limited to the application site and were consistent with physical trauma (pulling or plucking) to the hair.
Conclusions and clinical importance: Microscopic changes in the hair follicles of affected cats were consistent with self-induced trauma or barbering behaviour. All changes were reversible and paralleled findings associated with well-established, topical flea control products.
© 2013 ESVD and ACVD.