Anaphylaxis: Recent advances in assessment and treatment

Pathogenesis of anaphylaxis: mechanisms and triggers, cells, mediators, and organ systems. Human anaphylaxis usually occurs through a mechanism that involves cross-linking of IgE and aggregation of high-affinity receptors for IgE on mast cells and basophils. Common triggers include foods such as shrimp and peanut; medications such as penicillins, cephalosporins, and other β-lactam antibiotics; insect stings; and natural rubber latex. Other immunologic mechanisms that do not involve IgE are less commonly implicated and less definitively proven; however, humans experience IgG-antigen complex–mediated anaphylaxis (not shown) and anaphylaxis involving complement system activation and coagulation system activation, as exemplified by OSCS-contaminated heparin-triggered anaphylaxis. Nonimmunologic triggers include exercise, cold air, and some medications such as opioids. On activation, mast cells and basophils release more than 100 chemical mediators of anaphylaxis, only a few of which are listed. The diagnosis of anaphylaxis is based on a history of exposure to a triggering agent or event, the time elapsed between exposure and symptom onset, and the evolution of signs and symptoms over minutes or hours, usually in 2 or more body organ systems. Adapted from Simons.¹⁵

Prevention of anaphylaxis in community settings. Patient-specific risk factors should be appropriately assessed. Optimal management of comorbidities such as asthma, cardiovascular disease, and mastocytosis/clonal mast cell disorder is critically important. The benefits and risks of concurrent medications, especially β-adrenergic blockers, should be assessed, discussed, and documented. Other preventive strategies are trigger specific. Vigilant avoidance of confirmed relevant triggers is fundamental. The Web sites listed provide up-to-date, consistent patient information about allergen avoidance. Currently, immunomodulation is only used to prevent anaphylaxis from a few triggers. In patients with medication-triggered anaphylaxis in whom an alternative agent cannot be substituted effectively and safely, physician-monitored desensitization is useful. In most patients with stinging insect-triggered anaphylaxis, a 3- to 5-year course of subcutaneous venom immunotherapy is life-saving. For patients with frequent episodes of idiopathic anaphylaxis, a 3-month trial of prophylactic treatment with an oral glucocorticoid and a nonsedating H₁-antihistamine is recommended (see text for details). In the future, oral immunotherapy might be used to prevent food-triggered anaphylaxis, and anti-IgE antibody might be used to prevent anaphylaxis from a variety of triggers, as well as idiopathic anaphylaxis. Adapted from Simons.¹⁵

The effects of epinephrine (adrenaline). Through the α₁-adrenergic receptor, epinephrine leads to vasoconstriction, increased peripheral vascular resistance, and decreased mucosal edema. These actions are unique among the medications used for the treatment of anaphylaxis in the community. They lead to prevention and relief of obstruction to airflow in the larynx, as well as the lower airways, and prevention and relief of hypotension and shock. The pharmacologic effects of epinephrine are biphasic; for example, at low doses, it potentially leads to vasodilation and increased mediator release. Adapted from Simons.⁸⁵