I’m curious too. I was given penicillin about 20 years ago, when I had a very bad flu and complications. After a few days on it, my knee joints started swelling up. I told the doc, and he got me off the penicillin.
I’ve never known if that was an allergy or not, but have assumed on the safe side that it was.
Penicillin gives my stomach hell.
Ever since a “possible” allergic reaction to Amoxicillin 20 years ago no doctor will prescribe any in the class and instead I’ve been routinely prescribed Cefaclor, Ceclor, and Keflex with the latter also rendering a possible reaction after having been fine with it prior. This article reminds me I should go get tested. I have expressed my interest in doing such but it’s been blown off by my health care providers. I have a definite allergy to the Tetracycline class, prescription antacid, and also contrast dyes so it is possible there’s an autoimmune disorder or something.