Corticosteroid drugs
like prednisone, drugs used to fight cancer or chronic allergies (ref) And, possibly nibs similar to
Apoquel (ref) or mAbs,
like those under development for dogs.
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.