Certain medications the dog might be receiving concurrently (spinosad / Comfortis ®, antifungals medications like
itraconazole and ketoconazole, certain antibiotics, corticosteroids, Apoquel ® / oclacitinib, etc.) can
make a bad reaction to the avermectins more likely You can read more on the subject of demodectic mange treatment here, here, here and here.