I would not use ivermectin, since SafeGuard is proven to work against most chicken worms except tapeworms. Yes, you can use ivermectin and Corid at the same time time.
In your previous thread, @coach723 really gave you a good explanation of intestinal shedding. She didn’t think that it sounded like coccidiosis. Many vets will perform a fecal float on fresh droppings, if you call them first to make sure. But worming may actually be less expensive.
What do you suspect is wrong—coccidiosis, worms? Ivermectin is said to have lost some effect against worms, due to past overuse for mite treatment. It has an egg withdrawal time. SafeGuard 10% will treat most chickens worms with a dosage of 0.25 ml per pound given orally for 5 consecutive days...