Category: Drug Allergy  

Penicillin Allergy

The majority of people (well over 90%) who believe they have  a penicillin allergy pass an allergy test to the drug and can take penicillin.   Why is that?  Some people were never allergic (symptoms attributed to the penicillin were caused by another condition).  Others were allergic but no longer are.  A simple office based test for penicillin allergy is very reliable.

Question: Why is penicillin skin testing so important and who should we test?

Answer: Penicllin allergy can restrict you from taking a range of antibiotics.  Patients allergic to penicillin are also often not prescribed a related class of antibiotics (cephalosporins) which crossreact to some degree with penicillins.    Another issue  is antibiotic resistance.   Knowing that approximately 90% of patients labeled allergic to penicillin can safely take this antibiotic, testing for penicillin allergy, goes a long way in decreasing the use of the newer antibiotics, which are more expensive, often more toxic, and lead to resistance to these more potent antibiotics. Women of child bearing age who have a history of penicillin allergy should also be tested since Group B strep carriage requires treatment in the perinatal period.  Although treatment with the third generation cephalosporin is effective for Group B strep many women with a history of PCN allergy are instead treated with Vancomycin or Clindamycin (and Clindamycin resistance is an emerging problem with Group B strep).  Dentists also often prescribe Clindamycin for penicillin-allergic patients but this alternative antibiotic may wipe out too many healthy intestinal bacteria leading to severe diarrhea (C. Dificile colitis).