Immediate allergic reactions to β-lactams: Diagnosis and therapy

β-Lactams are the antibiotics which most frequently provoke adverse reactions mediated by specific immunological mechanisms. These reactions, classifiable as immediate or non-immediate, can be produced by the four classes of β-lactams (penicillins, cephalosporins, carbapenems and monobactams) currently available, which share a common β-lactam ring structure. Immediate reactions occur within the first hour after drug administration and are characterized by urticaria, angioedema, rhinitis, bronchospasm, and anaphylactic shock. Immediate reading skin tests are the quickest and most reliable method for demonstrating the presence of β-lactam specific IgE antibodies. It is crucial to use in diagnosis the suspected β-lactams themselves, particularly cephalosporins, in addition to penicillin determinants. Serum specific IgE assays can be used as complementary tests. Negative test results should be interpreted in light of the time elapsed from the last exposure to the responsible β-lactam. In fact, both in vivo and in vitro test sensitivity is known to decrease over time. In some diagnostic work-ups, patients with a positive history and negative skin and in vitro tests with classic reagents undergo a controlled administration of the suspected β-lactam. The management of immediate allergic reactions should take into consideration their severity and type. Adrenaline is the drug of choice in the treatment of anaphylactic shock. In addition to adrenaline, corticosteroids and antihistamines should be administered. Histamine H₁ receptor antagonists are the mainstay of the treatment of immediate allergic reactions such as urticaria, rhinitis and conjunctivitis.