Abstract: Objective To warn against potential delayed large-area allergic skin rashes as an adverse reaction during the combined treatment of severe allergic asthma using omalizumab injection. Methods One case of delayed onset allergic large-area rash occurred during the treatment of moderate to severe allergic asthma with omalizumab injection. The possible drugs responsible for the adverse reaction and countermeasures were identified based on adverse reaction correlation analysis. Results The adverse reaction in this patient manifested as a delayed large-area allergic skin rash. After such factors as the patient’s condition and concurrent medication were ruled out, the injection of omalizumab was considered to be the cause of the severe skin rash. The adverse reaction correlation was evaluated as “definite”. Immediate discontinuation of the medication and appropriate symptomatic treatment led to the patient’s recovery without any residual effects. Conclusion In clinical practice, delayed adverse reactions caused by omalizumab injection have to be monitored and immediate measures taken to prevent serious consequences.

Key words: omalizumab injection, delayed anaphylaxis, allergic asthma, skin allergic reactions, rash