Testing for penicillin allergies.
Had a penicillin allergy as a kid? You probably don’t now.
To prove a penicillin allergy exists, we skin test with penicillin and one of its breakdown products. You will be tested with what we call the major breakdown product of penicillin (commercially available as PrePen), plain penicillin and in some patients, ampicillin or a cephalosporin. In addition, skin testing with salt water (to which no one should react) and histamine (to which everyone should react) is used to help distinguish between negative and positive skin test reactions. Test agents are placed on the forearm and then scratched with a small plastic disposable peg. A positive reaction will look like a mosquito bite at the site of the scratch.