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In my training for penicillin skin testing, we used penicillin G 1:100 and 1:10 concentrations for intradermal testing. I have discovered in private practice that undiluted pen G is used, but seems to be very irritating so far. Is there a known non-irritating concentration of penicillin G? Is it not actually irritating for most patients (I haven't done a lot of these after entering practice)? I find it difficult to read results of these intradermal tests, but now wonder if negative intradermal tests of diluted penicillin G are sufficiently sensitive.


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

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