Will he follow his food out of the kitchen?
I've "trained" Tufty to come for his dinner by tapping the side of the tin bowl with my fingernail - when he's there I tap the bowl before putting it down for him. I can get him to follow the "tap tap" through the house when he's hungry. When he's not there (if he's in earshot) I tap the bowl he'll come running (well, scurrying - Tufty can't run because of his dicky shoulder).
It might be worth setting up a little dinner gong like this for Lupin, that he will associate with nice grub, and hopefully mean you'll be able to move him around the house willingly instead of his current stubbornness.
As for his stinky poos, while Panacur (fenbendazole) is one of the recommended treatments for Giardia (one of the suspected causes of chronic stinky diarrhea), it is by no means the only one, and cats do appear to be more resistant to treatment of Giardia than dogs, so just one, three day "session" may not be enough to cure Lupin, if this is his problem. I would call the vet tomorrow if Lupin is still the same, and ask how quickly to expect an improvement.
Just a note - I caught a couple of DR Mike Richard's articles on this subject, he recommends testing for FIV and FELv if resistance to treatment continues as he has found these conditions responsible for exacerbating the symptoms of the infection. Don't be offended if your vet recommends these tests, there is a scientific basis for them if he continues to be resistant to treatment.
I imagine your vet's next step will be a fecal sample inspection (or possibly several samples - as the cystic discharge associated with Giardia occurs sporadically so may not be apparent in the first specimen you take) to ascertain what strain of infection he has, after which there's a range of options to try, any one of which may work for Lupin.
As for his hunger, has the vet said he can snack between meals? Can you give him a handful of the sensitive biscuits every now and again to stave off his hunger? Sounds like he's getting stressed with his hunger. A young, boisterous kitten will naturally eat tons to keep his blood sugars level (and his temper).
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