I don't think the Iodine is bad for the dog, but it may have stirred up something which aggravated the joint pain the dog has.
About six weeks ago I pulled a muscle in my lower back while "cheating" my last curl up while weightlifting. I know lower back muscles are slow to heal and expected it to be sore for a couple of weeks. Well after three weeks of pain and plenty of Acetaminophen and Ibuprofen, I thought I was well enough to mow the grass. Anyhow I sent my back muscle into intense pain and spasms, to the point where my regular NSAIDs just couldn't touch the pain. I laid down, Iced, and spent two days on Naproxen Sodium recovering back to a tolerable pain level. Then I got some Serrapeptase, mainly for other purported benefits. I took one (Doctor's Best)120,000 unit capsule, in the morning, and had only the slightest reminder of pain all day long. The next day was the same. After five days of taking Serrapeptase I took a couple of days off and the pain started coming back, so I've been back on it for a couple of weeks now. I believe my back is healed, because I've been able to finally resume weightlifting without feeling pain in my lower back.
The reason I took a couple of days off was because I was feeling slight pain in my knees and an ankle I'd injured years ago. But I read that like Iodine, Serrapeptase can sometimes give a little discomfort while undoing many years of damage,to allow things to heal correctly. Overall I think it is great. I've tried an awful lot of supplements and Iodine has helped me greatly. Serrapeptase worked like a miracle for me. Although I've been gradually improving my health while exploring supplements Iodine, and Serrapeptase are two of the very few that I think I can be certain have been well worth my money and made age defying improvements in my body.
I've heard that Serrapeptase works well with animals too.
I got a bit gassy the first couple days I took Serrapeptase, (might have reacted with all the whey protein I was taking) but my body adapted and then I got some Syntol and that seemed to help also.