Penicillin allergy testing can safely exclude IgE-mediated penicillin allergy.
Almost 8% of the U.S. population claims to be allergic to penicillin, but only a small proportion of these patients are truly allergic. Penicillin skin testing is the only way to identify IgE-mediated allergy (an immediate hypersensitivity reaction mediated by preformed IgE bound to the surface of mast cells and basophils). Penicilloyl-poly-lysine (Pre-Pen), the major determinant of penicillin allergy, has been available commercially since 2009, but clinicians rarely order skin testing. Some physicians are concerned that Pre-Pen testing is inadequate without also testing for minor determinants (penicilloate and penilloate), which are not readily available.
From 2010 to 2012, 500 patients with histories of penicillin allergy (based on diagnoses recorded in their records) were skin tested in a California allergy department using penicilloyl-poly-lysine and fresh penicillin G. Negative tests were followed by oral challenges with amoxicillin. Four patients reacted to one of the two skin-test agents, and another four exhibited positive objective symptoms after oral challenges. None of these reactions [were] life threatening or required epinephrine.
In this study, fewer than 1 in 50 patients with penicillin allergy histories were truly allergic. We should stop accepting penicillin allergy history as a reason for lifelong avoidance. All drug reactions should be documented carefully. Patients with severe delayed reactions such as Stevens Johnson syndrome, drug reaction with eosinophilia and systemic symptoms (DRESS), or hemolytic anemia should never be challenged or tested; those with mild delayed reactions probably can undergo oral challenges. For those with potential IgE-mediated reactions (i.e., hives, edema, or other symptoms of anaphylaxis occurring within 1–2 hours), penicillin testing followed by oral challenge is safe and effective. Penicillin is the only antibiotic for which such testing is available.
Macy E and Ngor EW. Safely diagnosing clinically significant penicillin allergy using only penicilloyl-poly-lysine, penicillin, and oral amoxicillin. J Allergy Clin Immunol Prac 2013 May; 1:258. [J Allergy Clin Immunol Prac article abstract]Dr. Irena Veksler of Allergy & Asthma Care of Fairfield County comments: "This reinforces what we have long known - most patients with a history of possible penicillin allergy turn out not to be allergic. With increasing resistance to antibiotics, and overuse of many newer antibiotics, it is important to have penicillin antibiotics available as an option in as many patients as possible. All patients with a history of possible penicillin allergy should consider penicillin testing."