Dentists Failed medical students. Mumble.

He should have asked you as well as referring to the notes as 'allergic' can mean different things to different people.

I'd take the drug back, point out the error and see what they say first, I'd also ask for a copy of the form you filled in when you do as that might get 'lost'.

In terms of suing well you are in America and you can probably sue him for breathing, but in the UK you would need to show some effect of a negligent act really. First thing is to get a copy of everything and if you are serious get a Doctor to certify an allergic reaction and provide a copy of any records showing you have an allergy. If you suffered absolutely no effects you are possibly on shakier ground but there would probably be something in it. At the very least you need new antibiotics as the larger risk at present would be a worsening infection because you cannot take the drugs you were given. If they give you a replacement set of meds for free don't sign anything when you collect them without reading it carefully - you could find later you signed a waiver to forget it as you got a new prescription for free.