Update on biphasic anaphylaxis

Purpose of review Biphasic anaphylaxis is a well documented complication of anaphylaxis, but it has been inconsistently defined in the literature. Analysis of contemporary studies of biphasic anaphylaxis based on modern definitions is needed. Recent findings The rate of biphasic reactions in contemporary literature ranges from 0.4 to 14.7% depending on the study population. Observational studies have reported risk factors associated with the development of biphasic reactions; however, findings have been inconsistent and of questionable generalizability. Although life-threatening biphasic reactions are rare, up to 50% of biphasic reactions will require treatment with epinephrine. Early epinephrine administration may have a role in prevention of biphasic reactions, but the role of steroids needs further investigation. The optimal duration of observation is yet to be determined. Summary Given the relative rarity of life-threatening biphasic anaphylaxis and the new context of the NIAID/FAAN standardized definition, further research regarding biphasic anaphylaxis is needed to better elucidate the care model for anaphylaxis patients with a focus on: prevention of biphasic reactions; identification of patients at increased risk of a biphasic reaction; determination of appropriate observation strategies for anaphylaxis patients; and patient education and preparation for management of potential biphasic reactions.