Leopard Gecko Parasite Killers?

I've done my research, quite a bit of it. I'm considering buying some anti-parasite meds from petsmart for my sick 4 month old leopard gecko female. I know she has an intestinal parasite, confirmed from a pet vet and my own knowledge of little blue-ish black spots in gecko tummies. Now, the ingredients that I believe I need (and are in this anti-parasite med) Are Limestone (scoring the parasites causing them to die) Metronidazole and Fenbendazole, I know these two ingredients are active in vet meds, though I'm not sure why. I was wondering if anyone had any clues, I havnt gone to buy the meds yet, so I dont know how much to administer. I'm just concerned about wether this will work or not. That along with dusting her crickets that she eats (and soon there-after throws up right now) and a syringe for administering the meds that I usually use to give her repta-aid. I think this will get her healthy again, though I'd like some Serious(!) feedback on this method.