Ivermectin is a very effective drug but with a much narrower margin of error then fenbendazole. The dosage must be quite precise and for this reason it is often not recommended for small reptiles (under a pound). The panacur can be mixed with food because, unlike a number of other meds, it has little taste. Every blue tongue that I have worked with has loved canned cat food as an occasional treat. I would try mixing the panacur paste into a small amount of that to administer it. What is the skink being treated for exactly?