Can I use Betadine or Hexomedine on a cat's wound?

Well, you definitely did the right thing taking them to the vet. Let's see what happens once the jab wears off.

I've just got back from the vet’s; he gave him a steroid jab along with something else to stop him scratching and prevent any infection. We aren't sure of the cause yet—his ears are clean, so it’s not an ear infection. Maybe a spider bite... or perhaps an allergy to the new dry food I’m gradually introducing? The vet doesn't think so, as the irritation is quite localised. The jab should last until the middle of the week, so we’ll see if the scratching starts up again, assuming it stops at all! ;) Personally, as it’s on the same side as his microchip, I reckon he woke up, noticed something felt a bit different, and started scratching right at the base of his ear since he couldn't quite reach his neck! And once you start scratching... you just can't stop! A bit of a stress response, I suppose.

Civa, Yes, Betadine or a veterinary iodine solution is the same thing! My vet uses it too! I do think it's itching him a bit, but keep an eye on the wound. Did the wound appear because of him scratching at it? Laurence and her Noah’s Ark

Betadine. It's what the vet uses.