Less common side effects include:

• Hives, itching or skin rash.
  
  

  

• Swelling of the face, throat, tongue or lips (angioedema).
  
  

  

• Headache.
  
  
• Dizziness.
  
  
• Ear pain.
  
  
• Leg pain or arm pain.
  
  
• Joint pain.
  
  
• Fatigue.
  
  
• Malignancy (an abnormal growth that tends to invade and damage surrounding tissues). Several types of cancer were seen in patients receiving anti-IgE antibody treatment in clinical studies.  
  
  
• Anaphylaxis. A severe allergic reaction affecting two or more body systems. Without prompt emergency treatment, anaphylaxis can quickly progress to life-threatening anaphylactic shock, which is characterized by difficulty breathing due to constricted airways and a dangerous drop in blood pressure. Symptoms of anaphylaxis may include:
  
  
  • Hives
  • Severe shortness of breath
  • Tightening in the chest or throat
  • Swelling of the throat or tongue (angioedema)
  • Choking
  • Loss of consciousness

Anaphylactic reactions to omalizumab typically begin within two hours of receiving the drug. However, patients may experience a delayed reaction occurring anywhere from two hours to 24 hours or longer after receiving the drug.

Individuals who suspect that they are experiencing an anaphylactic reaction should seek emergency medical attention immediately. Those experiencing less serious side effects should consult their physician.

Research into anti-IgE antibody treatments is ongoing, and many of the long-term side effects of this type of therapy are still unknown.