Panacur is a good worm medication and isn't too hard on their gastrointestinal tracts if you give probiotics along with the Panacur. Since he doesn't have a bacterial infection, you can give whichever probiotic you are planning on giving him just prior to giving the oral Panacur, the probiotics won't interfere with the Panacur and will coat his stomach and keep the Panacur from making his stomach upset, and should help his appetite as well. I recommend either a non-dairy acidophilus, or a probiotic and digestive enzyme combination pill, crushed into a powder and given in baby food/Pedialyte slurries. As far as the mites, it depends on exactly what mite the vet identified on him, and what protocol the vet gave you, as some species are very difficult to get rid of.
You'll absolutely need to get the meds ASAP, especially the Panacur, as roundworms will keep his appetite at bay and it will continue to decline, but more importantly roundworms steal all nutrition he is willing to eat from his gastrointestinal tract, so he will eventually start losing a good amount of weight as he continues to eat less and less, and the roundworms not only multiply quickly but will be leeching all nutrition (calories, protein, fat, etc.) and all calcium and other vitamins/minerals from him, resulting in continually higher weight loss, lack of appetite, and eventually nutritional deficiencies and resulting diseases and conditions, such as MBD and Vitamin B1 (Thiamine) deficiency disease, which has symptoms that mimick MBD, such as twitching, muscle weakness, paralysis, etc. So get the Panacur going IMMEDIATELY, and you'll also need to completely disinfect his entire enclosure both inside and out, along with everything inside his enclosure, all decor, and with the mites you'll need to even disinfect his lighting, light fixtures, anything and everything touching him or his enclosure. I would get some F10SC disinfectant from your local pet shop, or order it and in the meantime use plain bleach, soaking everything in a mix of bleach and very hot water, and then rinsing everything very well until all traces of the chlorine smell are gone. You'll need to do this complete disinfecting of everything at least once a week (every other day is better because he can just keep reinfecting himself even while on the medications) and use disposable paper towels as his substrate, throwing them away and replacing them a few times a day until he's finished the medications and the roundworms are confirmed as being gone by a repeat fecal testing, and the mites totally eradicated by examination and repeat skin scraping test (I'm assuming your vet diagnosed the mites by skin scraping test)...It's a nasty combo he's got and it's going to be very frustrating to keep one or both of the bugs from reinfecting him and his enclosure. But you really need to get him started on the Panacur immediately, as it's been awhile now since his diagnosis and the worms are going to get bad enough to start leeching him of all nutrition and he's going to start losing weight and developing deficiencies.
