Drug Hypersensitivity

Drug therapy requires an understanding of the fine line between the beneficial and harmful effects of the drug. While the majority of adverse drug reactions (ADRs) are predictable, drug allergies are difficult to foresee, hence their designation as unpredictable ADRs. Drug hypersensitivity reactions can be a significant source of morbidity and mortality in clinical practice. Drug allergy labels can also prohibit patients from receiving first-line therapies, and therefore, previously diagnosed drug allergies should always be questioned. Any drug is assumed to be capable of eliciting these types of reactions; however, the frequency differs widely with antibiotics being the most common offender. Multiple factors play a role in the risk and severity of reactions including the class of drug, dose, administration route, frequency and duration of exposure, and the genetic predisposition of the subject, particularly with human leukocyte antigen B (HLA-B) alleles. Beyond a thorough clinical history, the tools available for identifying and diagnosing hypersensitivities are currently limited; however, accurate diagnoses are still possible and important to help protect patients from re-exposure to the culprit medication. Given the high morbidity and mortality associated with drug hypersensitivity reactions as well as the increased failure rate with second- or third-line therapies, appropriate evaluation by Allergy & Immunology specialists is imperative.