Anaphylaxis and biphasic phase in Thailand: 4-year observation

Anaphylaxis, a severe systemic allergic reaction, can be fatal. However, its prevalence has been underestimated especially in biphasic phase, due to a lack of case awareness. This study aimed to determine the rate of anaphylaxis, describe clinical manifestations and management, and identify the causative agents and risk factors of biphasic anaphylactic reaction.

An observational study was conducted at the Emergency Department of Thammasat University Hospital, Thailand, during the period 2004-2008.

Of total 208 cases of anaphylaxis identified, the median age was 20.67 years; 52.9% were male. The anaphylaxis rate was 49 per 100,000 patient-years. No fatal case was found; 58.7% had a history of atopy, and 38.5% had experienced a previous allergic reaction, of whom 8.8% had had a previous anaphylactic reaction. The causative allergens were identified in 82.2% of cases; food allergy was most common. Urticaria was the most common presentation (87%). Among 6.3% of the patients who developed biphasic reaction, a significantly longer time from onset of symptoms to administration of epinephrine was detected, with a median of 240 minutes for those with biphasic anaphylaxis, versus 70 minutes for those without (p = 0.002). The median times from onset to hospital arrival and the arrival to administration of epinephrine were also significantly longer in the biphasic group than the non-biphasic patients (p = 0.002 and p = 0.001, respectively). In multivariable regression models, the time intervals from onset and hospital arrival to administration of epinephrine continued to predict biphasic phase occurrence (p < 0.01).

Anaphylaxis predominantly occurs among children and young adults. Delayed administration of epinephrine was associated with the occurrence of biphasic anaphylaxis.