Skin Supplement for Extended Flea Protection. CapShield Plus is a combination of Nitinpyram and Lufenuron. Lufenuron is a growth inhibitor (IGR) that will stay in the blood stream about 30 days. Any new fleas that get on the dog after the first day and take a blood feed will not fully reproduce. Capshield Plus is the only way to introduce a long-term IGR into the animal’s environment as sun breaks down IGR in yard sprays within a day.