one of the most effective and safer to use drugs on bearded dragons. It is also one of the main drugs that breeders and rescues use to "shotgun" treat animals since is is effective the the side effects rare if any. Ideally you would have fecal's done on a single pet, but we you get 10-20 in a week that is a bit cost prohibitive so breeders and rescues will treat them and then watch to see who still has problems... thats called shotgunning.
Yes, it is normal to have a change in their feces while on this, it is actually killing the worms in their digestive tract and making them pass through the digestive system. Hence the beardies system is digesting them.
Depending on the worm they have, it can also in extremely large infestations, cause such a mass die off that they become constipated, because the drug does work so well, so you have to keep them well hydrated during treatment. If they did become impacted, a few drops of a vegetable oil will usually work to help them pass it through.
The first dose of panacur kills the adults, the second dose is to ensure that all were got and to kill off the ones that hatched since. Some vets prescribe a third dose to make sure any the dragon has ingested during treament are killed also.
Parazap and other preventative I agree have their place, and I do use them, but when you are working with a dragon that is heavily loaded or showing other signs the parasites or worms are affecting them, I do not hesitate to use the medication. I have seen too many pathology report of the damage that untreated parasites and worms can cause in bearded dragons to take that risk.
Many people who contact us thinking they may have yellow fungus disease, actually have coccidia or worms that have entered organs or most commonly the bile ducts of the liver and that is what is causing the yellow in the dragons, we ALWAYS have them have the animals checked for those first and I have never seen where anything but drugs will get to those and those are the ones that will be fatal if not treated.