The Evolution of Our Understanding of Penicillin Allergy: 1942-2022.

This article reviews our evolving understanding of penicillin hypersensitivity at the 80th anniversary of penicillin's clinical introduction. Penicillin breakdown products covalently bond to serum proteins, leading to classic drug hypersensitivity. Penicillin remains the most frequently reported drug "allergy." Adverse reactions were presumed, in retrospect incorrectly, to implicate a risk for anaphylaxis, and therefore skin testing for IgE became the focus. Skin test positivity may wane over time. This insight has led to the radical conclusion that penicillin hypersensitivity may not be "forever." Atopic background, other drug allergies, family history, gender, and race are apparently not risk factors for penicillin hypersensitivity. Confirmed penicillin hypersensitivity has declined since the 1960s, potentially due to "cleaner" penicillin products and lower dose oral, instead of parenteral, use. Avoiding penicillins, without evaluation, caused unanticipated problems that have been appreciated only recently including longer hospital stays, increased cost of care, suboptimal outcomes from serious infections, and greater toxicities and costs with alternative antibiotics. There are personal and public health advantages with broadly implemented penicillin allergy delabeling based on a reaction history-based risk assessment. Limited skin testing followed by an oral challenge, if negative, for higher-risk histories, and direct oral challenges in lower-risk individuals are currently the reference standard tests to confirm current tolerance.