This thread is really interesting. I actually have a dog on levothyroxine, but she's not really responding to it. Not that I can see, anyway. She's been on 700mcg 2x/day for a long time now, yet she's still obese, still has a poor coat, still loses patches of hair sometimes, is still snarky with the other dogs (sometimes a symptom)....the works. She was checked, diagnosed with hypothyroidism, prescribed the levothyroxine, took it for about a month, then re-checked to see if the dosage was correct.. Everything was done by the book, and the 2nd test confirmed the dosage to be correct.. They said her 'levels' were 'within range' after the med.
Now I'm wondering A) levels of what, and B) how "within range" was she?
She seems to maaaaybe have a bit more energy, but I dunno... She only eats 2 level measuring cups of food a day and somehow maintains about 65lbs on a frame built more for about 40-45.. She's very, very tubby. She went back to the vet several months after starting the med and I was told that some dogs simply didn't shed the weight on levothyroxine...I was offered no explanation as to why, though.
I started reading some of y'alls comments on T4 vs. T3, and it got me thinking.. I've had cause to investigate several human problems related to genetic mutations and so forth, and it seems pretty common for people to lack working genes necessary to the conversion of certain chemicals into other chemicals.. To lack the genes to properly convert T4 to T3 isn't much of a stretch, I don't think...indeed, I'd bet there's a mutation involved somewhere if someone takes -- or an animal is administered -- T4 and doesn't get better.
I think I may have a talk with my vet about Liothyronine.. Apparently, someone makes it in a vet scrip called "Cytobin," and I wouldn't doubt it's been around long enough to have generics.
Obviously I can't spend a fortune on meds if it's super expensive, but....definitely worth a conversation.
Again...very interesting thread.