Thanks everyone.
Regarding Convenia, I'd rather have the inconvenience of putting drops in food a couple of times a day. I did this when they were little and had flu. It's no problem to do. George ate his Metacam-dosed food very readily on saturday evening, though I had to sit with them while they were eating to ensure that only George ate from that dish. Simples. Pilling him, however, would be a nightmare of claws.
But the Convenia is in his system and can't be got out, this time. From what I've read, the main problem with it is that it stays in their body for a month, which means that if they have an adverse reaction it's a long time before the cat is back to normal. Whereas the shorter-acting antibio's are out of the system more quickly, enabling a faster return to health.
George doesn't seem like he's in pain. He's eating again and active. After I gave him his Metacam on saturday, he became apathetic and subdued, just as he was when ill.
I've changed my mind about my course of action. If the Metacam WERE antibio's, I'd give them as normal, but as they're only painkillers and he doesn't seem in a lot of pain, I'm not going to give him any tonight. Of course, it's possible that he appears well because of the Metacam.
I'm thinking of it as an equation: painkiller vs possible renal failure. I think I'll let him put up with a headache rather than develop renal problems.
The antibio's seem to be working, though I'd have preferred him to be given a shorter acting one and drops for his food.
Gillian, hope Harry gets better soon, at least your vet went to the trouble of testing his kidney function first, especially after the problems with you other cat.
Angie, one of the reasons metacam was developed was for post-operative pain. George hasn't had an op since the snip. He did seem "spaced out" after I gave him his first dose.
Rosella, I don't know how reliable it is, but there's lots of anecdotal evidence against the use of Convenia; people saying how their cat became blind, unwell, and even died. Of course, the cat would have been ill anyway. But I read so much of the same thing, it can't be coincidence. Thanks for your kind thoughts. He looks like he'll recover soon. I'm trying to keep a close eye on him, but he's insisting on going out. The vet suggested keeping him in but not isolating him, which meant keeping the whole tribe in. I gave them litter trays, but Pebbles expressed his thoughts by pooping in my bedroom.
I think going out is probably good for his morale and health.
Thanks lots for the input