Presume you mean Frontline spray for lice and fleas Roisin. We use it for neck lice at 3 sprays per Kg. The dose can't be repeated for 28 days it says on the packet so perhaps that's a sensible egg withdrawral period. But we have covered this topic recentlt and it appears only the spot-on enters the blood stream, which is why it kills chickens as even at one spot the dose could be too high. But you can get the spot-on anywhere, the spray is vet prescription only. Expensive treatment and I'm not sure it would work on red mite as they are not resident on the chickens for very long -just enough to drink full of blood.