Biphasic anaphylaxis is a well-documented anaphylactic complication, however it has been characterized inconsistently in the literature. It is necessary to examine current research on biphasic anaphylaxis using recent criteria. In the current research, the rate of biphasic responses ranges from 0.4 to 14.7 percent, depending on the study population. Observational studies have identified risk variables for the development of biphasic responses; however, the findings have been inconsistent and of uncertain generalizability. Although life-threatening biphasic responses are uncommon, up to 50% of biphasic reactions will necessitate epinephrine therapy. The best time to observe has yet to be established.
Given the rarity of life-threatening biphasic anaphylaxis and the new context of the NIAID/FAAN standardized definition, more research on biphasic anaphylaxis is needed to better elucidate the anaphylaxis care model, with a focus on: prevention of biphasic reactions; identification of patients at increased risk of a biphasic reaction; and determination of appropriate obs.