A single dose. I felt the effects about an hour afterwards -- I clearly remember all of my joints feeling way too hot, and my Achilles's tendon (which I later learned is one of the more common sites of injury due to Cipro) felt incredibly weak. My anxiety sky-rocketted, I was sweating profusely. My body clearly hated the drug.
I called the doctor and they advised that I stop taking it immediately, but clearly the damage was done.
I had no idea about any of the side effects. I was just a kid so I wasn't yet in the habit of researching drugs or (stupid!) even looking up which side effects are signs of a serious reaction. All I knew was I had a bacterial infection, had been given antibiotics a couple times before in my life without issue, so why worry?
I guess it's technically on me to read the literature, but again...I was a kid. I think this was the second time I'd ever seen a doctor without my parents present. A drug this serious should require a stern talking-to by the doc and written consent/understanding of the risks by the patient before it's prescribed. I know that had I been warned, I would've said "fuck no." Sure, I was a dumb kid, but even a dumb kid who is essentially a serious athlete (one who just happens to use really small muscles with an instrument rather than big ones) would've known that "irreversible nerve damage" isn't worth tempting fate.
There isn't a day that goes by without me regretting taking that pill. Again, I don't know the full extent of the damage, but I know that at least it ruined my career just as it was getting started.
Edit: What's really fun is that I may still be seeing new symptoms. I recently suffered Sudden Hearing Loss -- while I'm no longer a professional guitarist, I am a pro musician -- and of course the cause couldn't be pinned down (I know it's not due to loud noises, since you won't meet anyone more careful with their ears than me). This article stating that these drugs may be ototoxic is quite terrifying. My ears have been sort of deteriorating over the last year or so, and if it's Cipro continuing its reign of terror, I don't know what I'll do. File a lawsuit, maybe?