Thanks for the well wishes again, everyone.
One (or maybe all) of the injections Ted gave Charlie on Monday seems to have contained some magic serum, because once he calmed down on Monday afternoon he's been a different cat. He's eating normally, drinking normally, yesterday he jumped up on me a few times and had some lovely tickles and purred a lot and slept on me. He's completely calm. He still sulks under a dark, dusty chair out of the way, but in time I expect he'll be back to sleeping in the sun on the bed.
I took him back this morning and Ted was really amazed he'd sprung back so quickly.
If it was the penicillin that helped, it's likely because he either had hepatitis (apparently can be a secondary symptom of an overactive thyroid -- who knew?) or an infection that travelled to his liver from his gall bladder after having had a poorly tummy for so long. Either way, he gave him another shot of it this morning, and I'm to take him back on Friday to finish the course.
In terms of the B12, he said it's his favourite injection to give because years ago he was treating a cat that was inappetent, and he couldn't work out why after trying everything and looking for everything. He referred it to specialists at Liverpool in the end, and the first thing they did was give it a B12 shot, and it started eating again immediately. Since then it's a go-to thing he does if a cat is out of sorts for confusing reasons. It doesn't hurt if that's not the reason they're poorly, but it can make a big difference. Since Charlie had been having poorly poos for a couple of weeks it's entirely possible his gut wasn't producing the B12 he needed.
The anti-nausea injection likely just made him feel a bit better in general. Even though he wasn't vomiting he probably felt sick.
He's put on a little bit of weight over the last 2 days as well, which is great.
I'm so proud of the little bugger. It really is astonishing how quickly he bounced back. I just have to hope it lasts now. After Friday's visit we're hopeful he won't need to go back for a while. He'll probably need another blood test in about 3-4 weeks, just to check the thyroid isn't dropping too low, and to see if the liver enzyme levels are starting to come down. I think he'll be glad to have some peace and quiet. He was a lot calmer at the vet today, but on Monday Ted was saying when I left him he was in a complete state. I feel so sorry for the little thing, he'd been through so much.
There were 4 pets at the vet waiting with me this morning all called Charlie
Edit: oh, and I'm sure you're all dying to know -- yes, he did a normal poo this morning for the first time in 2 weeks