program plus for fleas and heartworm

I read through the other posts regarding fleas and I didn't see where anyone had mentioned program plus. The active ingredients are milbemycin oxime and lufenuron. It is an oral monthly pill for fleas, heartworm, hookworms and roundworms. I didn't know if anyone has used this before or knows anything about it. It looks like you need a prescription for it. I would like to try it. But I want to make sure it is safe. I have a 4 pound pomeranian and comfortis is for 5 pounds or more so I don't think he can use that. The topicals don't work on him his hair is so thick I can't get much on his skin. He still itches when I use them. He gets good relief with capstar temporarilly.