Frontline is not absorbed into the blood stream, so the eggs are safe..As for deworming I personally use valbazen and Safeguard goat wormer(fenbendazol) Valbazen- I mix 1 part Valbazen and 1 part water. using eye dropper I give 1 drop per pound of body weight. With fenbendazole I give 1 drop per pound undiluted, you can estimate weight as a lil more is not gonna hurt. I rotate these two with Levamisole sheep oblets. 2 oblets per gallon of water for one day.
As for how often, some ppl worm once a month, I personally worm every 3 months, as with any wormer, after first worming, worm again in ten days to get the ones that have hatched from the eggs left behind. these 3 wormers are not cleared for poultry, withdrawal time is not known, We always wait two weeks before eating the eggs after worming.