There’s quite a bit of information on the web about the internal use of iodine for urinary tract infections. See a list. Most or all of this info comes from naturopathic and holistic type folks, not from PubMed. I believe that in the old days, iodine in the form of tincture or Lugol’s was commonly used for urinary tract infections, but am unable to confirm this.
A couple days ago, my pet fish was obviously very ill, lying in the bottom of the bowl, hardly moving, refusing to eat. In fact, several times I had to to tap the bowl because I thought he was dead. This went on for maybe five days, and I thought he was a goner for sure. Thinking that he had a bacterial infection, and also that his death was imminent and not knowing what else to do, I put one drop of Lugol’s iodine in his water. I was also concerned that that amount of iodine might be toxic to him. Guess what, the next day he was much better, and as of today it’s like he was never sick.
Last year, a friend of mine who has pet rats asked me what to do when her rat started bleeding. Seems that the most common cause for finding blood in a rat’s cage is a urinary tract infection. She of course didn’t want to spend a huge sum on a vet. Her rat was very sick, and I figured that an infection like that could easily kill him, especially if it got to his kidneys. So I told her to go to the drugstore and buy some tincture of iodine, and add a couple drops to his water bottle. Again, I wasn’t sure about dose and toxicity. (Note the skull and crossbones that a bottle of tincture of iodine displays.) Anyway, it worked like a charm; cured the little guy.
Not recommending this, but it might be useful information.