Be carefull with the Tranq.- Ace esp. it slows down gut motility and can lead to impactions. Years ago I had good luck with vallium either pill or injectable for an old guy. It was nice because it stimulated his appetite, kept him eating and drinking, gives them a feeling of well being. Hard to get now-people abuse it.
Then fluphenizine (prolixin) was in vogue, it was very expensive.
I find switching to hay based diet/cutting way back on grain helps as much as drugs. May be a slow feed hay net, so he can munch while all the chaos goes on?
And a routine he can count on will help.