36.1 Fear and Labelling

It might seem unusual to think of penicillin (PCN) allergy as terrifying but when treating a patient with PCN allergy who has an infection, a lot of fear is generated. Some on the part of the practitioner (What can I use to treat the patient with? Are cephalosporins safe? What happens if the patient has a serious reaction?), and some on the part of the patient (My mother had a serious reaction to penicillin, she told everyone in the family not to take it!). It’s also an extremely difficult label to get off of a patient’s medical chart and will follow the patient around the health care system, even if incorrect. The author has come across patients who have got the label added to their chart even when they do not have any adverse reaction to penicillin, and they are afraid to remove it. Adding PCN allergy testing to a practice can help not only the patient, but also colleagues, and help reduce the overall cost of health care.

36.2 Serious Stuff

PCN allergy is classified as Type B (unpredictable) adverse drug reaction. It can manifest as any of the Gell and Coombs hypersensitivity reactions. Type I (IgE-mediated, immediate hypersensitivity) and Type IV (cell-mediated, delayed) reactions are the most common.

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  Type I IgE-mediated hypersensitivity typically occurs soon after exposure and includes hives, swelling, itching, and angioedema.

  
  
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  Type IV IgE-mediated hypersensitivity typically occurs toward the end of exposure and includes drug rashes, toxic epidermal necrolysis (TEN), and Steven-Johnsons syndrome.

Of the general population only 10% report an allergy to PCN and 90% are found to tolerate it.

36.3 History

How can a practitioner identify candidates for PCN allergy testing? Unfortunately, a practitioner has to talk to people and ask them questions. Here are some questions that are helpful to ask:

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  What type of PCN was given? What was the route of administration?

  
  
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  What was the reason it was given?

  
  
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  What was the reaction?

  
  
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  When in the course of the medication did the reaction happen? How long ago was it?

  
  
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  How was the reaction treated?

  
  
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  Have you had PCN since then? Have you had a cephalosporin since then?

  
  
  
  
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    Answers that are consistent with an IgE-mediated PCN allergy (hives, happened soon after starting PCN) are candidates for testing.

    
    
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    Many patients will not know what the reaction was (“I was an infant, my mother told me I was allergic”)] or will report he/she is allergic to PCN when never having taken it due to a family member having a PCN allergy. These patients are also potential candidates for testing.