Penicillin Allergy and the Return of Pre-Pen


Penicillin allergy is by far the most commonly reported drug allergy.  However, the vast majority of patients reporting a penicillin allergy cannot remember ever having had a reaction.  Most were told at some point, usually by a parent or grandparent, that they had a penicillin allergy and some even tell me that it simply appeared in their medical chart for unclear reasons.  A study once showed that in 20% of hospital admissions, the patient reported an penicillin allergy, but when these people were tested, only 10% of those reporting an allergy were actually positive.  So, 90% of people who thought they had a penicillin allergy didn’t!

In penicillin allergy, people can react to different parts of the penicillin molecule. These parts were named major determinants and minor determinants based on the frequency of reactions to the different parts.  In the past, testing to the major determinant was done using a commercially available product called Pre-Pen.  Unfortunately, Pre-Pen was taken off the market several years ago, leaving allergists with little to test with.

It was announced today the Pre-Pen is coming back.  Production is to begin this month, in fact.  The product information sheet states that a negative skin test with Pre-Pen gives a less that 5% chance of reacting to therapeutic penicillin.

Our office will be stocking Pre-Pen and performing skin tests and oral challenges in appropriate patients.  If you would like to find out if you are really penicillin allergic, let us know.

Dr. O


  1. It is true that penicillin have many side effects but the effects vary depending on the immunity of every individual who take in this medication.

  2. How would you know if you are allergic to Penicillin? Are there some signs like what happen to you if you are allergic to other seafoods?

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