Incidence and characteristics of biphasic and protracted anaphylaxis: evaluation of 114 inpatients.

AIM

Anaphylaxis is a systemic allergic reaction that potentially causes death. Most anaphylactic reactions are uniphasic, but some cases may be biphasic or protracted. However, these clinical epidemiology concepts are unfamiliar in Japan. Therefore, we have investigated the incidences and characteristics of patients with biphasic and protracted anaphylaxis.

METHODS

We retrospectively evaluated patients with anaphylaxis in a single emergency medical center located in Yokohama, Japan from April 2009 to March 2012. We analyzed the incidences and characteristics of patients with biphasic and protracted anaphylaxis who needed to be admitted.

RESULTS

A total of 253 patients were diagnosed with anaphylaxis and 114 patients needed to be admitted. Of the 114 patients, 103 (90.4%) were uniphasic, 7 (6.1%) were biphasic and 4 (3.5%) were protracted anaphylaxis. The most common antigens were foods and drugs. The median onset of a biphasic reaction was 8 h and dermatologic symptoms were mostly observed. Regarding severity, mild symptoms were seen in four cases, similar symptoms to the initial reaction were seen in two cases, and only one case was severe. The duration of protracted anaphylaxis varied from 2 to 8 days.

CONCLUSION

The incidence of biphasic and protracted anaphylaxis in inpatients was 6.1% and 3.5%, respectively. The median onset of biphasic reaction was 8 h, and most symptoms were mild or similar to the initial reaction. We suggest that patients with anaphylaxis need an 8-h and ideally a 24-h observation period in order to monitor possible biphasic reactions. The duration of protracted anaphylaxis was up to 8 days.