You are correct. Undiluted penicillin G will cause skin irritation. According to the 2010 Drug Allergy Practice Parameters, the recommended concentration of penicillin G to use for skin testing is 10,000 U/L. This dilution is recommended both for prick and intradermal testing. In order to attain the recommended dilution, it will require performing two serial 10-fold dilutions as the concentration of the stock bottle is 1,000,000 u/ml.
1. Solensky R, Khan D et al. Drug Allergy Practice Parameter. Annals of Allergy, Asthma and Immunology 2010; 105: 250.
I hope this question helps you in the care of your patients.
Jacqueline A. Pongracic, MD, FAAAAI