THURSDAY, Jan. 25 (HealthDay News) -- Biphasic anaphylaxis occurs in approximately 20 percent of patients experiencing such allergic reactions, with the second phase occurring as many as 38 hours later, according to a report in the January issue of the Annals of Allergy, Asthma & Immunology.
Anne Ellis, M.D., and James Day, M.D., of Queen's University in Kingston, Ontario, Canada, monitored all inpatient or emergency department patients in a tertiary care center who received a diagnosis of anaphylaxis or allergic reaction between 1999 and 2001. Of 134 patients identified, 103 were surveyed for symptoms and biphasic events.
Twenty of 103 patients experienced biphasic incidents, with the time to onset of the second phase an average of 10 hours later (range, 2 to 38 hours). Biphasic reactors took longer to resolve the initial incident than did uniphasic reactors (133 versus 112 minutes), and typically received less epinephrine and corticosteroids. Those whose initial incidents resolved in under 30 minutes had no incidents of biphasic anaphylaxis, while those whose first events took exceptionally long to resolve (193 minute average), were more likely to experience onset of a second allergic phase beyond nine hours.
"The findings from this study suggest that patients treated for anaphylaxis should be monitored for 24 hours or longer," the authors write.
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