Biphasic anaphylaxis: A prospective examination of 103 patients for the incidence and characteristics of biphasic reactivity

Abstract

Rationale To describe the incidence and characteristics of biphasic anaphylaxis occurring in a tertiary care center in Canada. Methods All emergency room visits and inpatients given a diagnosis of “allergic reaction” or “anaphylaxis” were referred. Patients were contacted to fully document symptomatology and determine presence of biphasic reactivity. Full chart review was completed, and uniphasic/biphasic cases were compared with the Mann-Whitney test for continuous data, and Fischer's exact test for ordinal data. Results 134 cases of anaphylaxis were identified over a 3-year period. Complete follow-up was obtained for 103 patients. The mean age was 33 years (range: 11 months–79 years). Twenty patients were established as being biphasic reactors (19.4%). Average time-to-onset of the second phase was 10h (range 2–38), 8 patients (40.0%) had their second phase occurring >10h after the initial reaction. The clinical presentations of uniphasic and biphasic reactions were similar, as were past histories of anaphylaxis/asthma. Time-to-resolution of initial symptoms was significantly longer for biphasic reactors (112 vs. 133 minutes, p=0.031). Differences in management were noted – biphasic reactors received less epinephrine (p=0.048), and tended to receive less corticosteroids (p=0.063). Conclusions Biphasic reactivity occurred with an incidence of 19.4%. The second phase onset was 10 hours on average, but occurred as late as 38 hours. The occurrence of biphasic anaphylaxis may be related to under-treatment with epinephrine and corticosteroids.