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Clinician’s Corner: Penicillin Allergies

“I’m allergic to penicillins. The last time I took Augmentin, I got horrible upset stomach and diarrhea.  I can’t take penicillins.”  This happens so frequently in our pharmacies; your Thompson Pharmacist would like to share some insight about drug allergies.

Over 30 million people in the United States report a penicillin drug allergy.

Less than 5% of these patients mount a type I hypersensitivity reaction mediated by IgE antibodies (i.e. anaphylaxis (shock), angioedema (swelling of throat and lips), bronchospasm,(shortness of breath) etc.). These are histamine-related mechanisms, which is why diphenhydramine (Benadryl)- an antihistamine usually helps relieve symptoms. Here is a table describing all of the penicillin family reactions

Table 1. Classifications of β-lactam Reactions

Levine Classification Gell & Coombs Classification Time to Onset, h Mediator(s) Mechanism Clinical Signs
Immediate Type I ≤1 PCN-specific IgE antibodies Histamine and vasoactive storm Anaphylaxis; angioedema; bronchospasm; urticaria (hives)
Non-immediate  

Type II

≥72 IgG, complement Antigen bound to hapten and fixed in tissue; increased clearance of RBCs, Plts Goodpasture’s syndrome; PCN-related hemolytic anemia
Type III IgG, IgM immune complexes Tissue deposition of immune complexes Systemic Lupus; Penicillin-induced serum sickness
Type IV T-cells Activated T-cells Morbilliform eruptions, contact dermatitis; Rarely more serious: e.g., Stevens-Johnson Syndrome

So, as we can see, penicillin allergies come in variations, with the Immediate Type-1 being the most serious.  Those are the ones that physicians and pharmacists need to be most concerned about.

So what’s the Big Deal… we have clindamycin and fluoroquinolones.  From head to heart to skin infections (notably methicillin-susceptible Staphylococcus aureus or MSSA), beta-lactams like cephalosporins and penicillins are the drugs of choice. If they are “taken off the table,” we are forced to use broad-spectrum antibiotics like clindamycin and fluoroquinolones (Cipro, Levaquin). Fluoroquinolones and clindamycin may not only be less effective for eradicating the bacteria (leading to antibiotic resistance), but also are a major cause of Clostridium difficile diarrheal infections!

First-generation cephalosporins are commonly prescribed for surgical site infection (SSI) infection prevention for almost all surgeries, either alone or as combination therapy. Preserving first-generation cephalosporins through antibiotic stewardship is critical to future patient care.

You Can Help to Set the [Allergy] Record Straight!

Almost 80% of patients with serious reactions lose their hypersensitivity after 10 years! Your Thompson Pharmacist will ask questions about your reaction symptoms, time since the initial reaction and whether you have taken other penicillin-like antibiotics since can be useful to “de-label” and remove allergies from your records.  Pharmacists must make sure that when we document a patient-reported “allergy,” we delineate between allergies and side effects:

  • Allergy is an adverse drug reaction mediated by an immune response (e.g., rash, hives).
  • A side effect is an expected and known effect of a drug that is not the intended therapeutic outcome (GI upset, diarrhea).

Your Thompson Pharmacist is interested in your healthcare by keeping track of important drug information as well as allergy information.  Trust your Thompson Pharmacist to help you get the best and most affordable antibiotic therapy.  Go Ahead and ASK…at Thompson Pharmacy it’s All for YOU!