Maybe your pet has an allergy to the frontline or maybe it irritates the skin. This is an unusual side effect in some animals. If the itch is as bad as you descibe I would not use the medication anymore. Why don't you try Advantage instead. This is the first time I got your question. Vetcare
You can try Benadryl 25 mg 2 x daily. I recommend a visit to the vet so the eye can be checked out. Good luck, vetcare