j_f, it seems it's worse than I thought before considering his age, but still I wouldn't give up early. Whatever his age be, don't think that he gave up and/or his organism doesn't try to recover. I know he might be in pain but most of the time in this kind of situations, there is this threshold they have to surpass, once he does it, he'll liven up.
Some great advice you got here, especially about supporting his morale condition. Though, thinking it'd be better him to take his pills, drink and feed a bit asap, seeking more help from vet would be my priority, I'd see a different vet too if necessary.
I hope he'll be better soon.