Objective To observe the occurrence and possible mechanism of allergic reactions of Xiyanping Injection in the real world. Methods The patients used Xiyanping Injection were monitored from September 2012 to October 2013 with a prospective

multi-center

large sample and registered method. An embedded nested case-control study was conducted to analyze the patients with allergic reactions. One allergic patient was matched with 5 healthy volunteers by taking gender and age ± 5 years as the matching factors. The blood samples of the patients and healthy subjects were collected. The immunoglobulin A（IgA）

immunoglobulin G（IgG）

total immunoglobulin E（TIgE）

complement 3（ C3）

complement 4（ C4）

interleukin-2（ IL-2）

interleukin-4（ IL-4）

interleukin-6（ IL-6）

interleukin-10（IL-10） and interferon-g（ IFN-g） were detected and analyzed. Results There was one allergic patient（male

90. 1 years old） in 4 023 patients used Xiyanping Injection. He was admitted to hospital suffering from pneumonia and bronchitis. His blood sample test results showed that the levels of TIgE

IgA

IgG

C3

C4 and IL-2 were within the normal range

IL-4 was slightly higher than that in the healthy group and the levels of IFN-g

IL-6 and IL-10 were significantly higher than those in the healthy group and normal range. Conclusion This study suggests that Xiyanping Injection may be associated with the occurrence of allergic reactions but the primary disease and age may be the influencing factors of allergic reactions.