I, too, don't see how IGF-1 can lead the body into attacking an antibiotic substance which it completely unlike a virus or bacteria. It's just a chemical really. I would think that increasing the body's immune response would only help the antibiotics do their job.
Normally, I might believe a doc with a background in endocrinology, etc., but my last endo was a complete total waste of my time and money. He didn't really know what he was talking about with respect to my hypoglycemia or HRT treatment and only wanted to save his own ass. That being said, not all docs are the same so I can understand if you trust your doctor friend, but as far as inhibiting the effects of an antibiotic, I would have to see a study on that first, and I'm pretty sure there aren't any considering IGF-1 is still relatively new.