Omalizumab ensures compatibility to bee venom immunotherapy (VIT) after VIT-induced anaphylaxis in a patient with systemic mastocytosis

Background: Systemic reactions and anaphylaxis due to Hymenoptera venoms occur in up to 7.5% of the European population. Fatal sting reactions are very rare. Serum tryptase levels should be measured in all patients with a history of severe reactions in order to detect mastocytosis and to determine the risk of severe reactions to venom immunotherapy (VIT). The risk to experience severe or even fatal anaphylaxis due to insect stings is quite high in patients with mastocytosis. Therefore, lifelong VIT is recommended in these highly threatened patients. Multicenter studies involving a large population report that up to 20% of patients undergoing VIT have intolerance and systemic reactions to immunotherapy. Some of these side effects occur repeatedly and cannot be managed by standard treatment. A pre-treatment with the anti-IgE antibody omalizumab was useful in many cases. However, omalizumab is not approved for the indication anaphylaxis. Therefore, there is still no defined protocol for omalizumab pre-treatment, and the optimal duration, dosage as well as long-time benefits are still unclear.

Case report: We present a 60-year-old female patient with mastocytosis who developed a severe anaphylactic reaction during initiation of bee VIT. Serum tryptase was elevated, and a KIT mutation D816V was subsequently confirmed. Component-resolved diagnostic tests revealed specific IgE antibodies to recombinant Api m 1 only. The patient was treated with 150 mg omalizumab, administered subcutaneously 5 weeks, 3 weeks, and 1 week prior to re-start of immunotherapy and for 2 months in parallel to VIT. Updosing was done by a 7-day rush schedule. During this period, no anaphylactic reaction developed, and the bee VIT was well tolerated with up to 200 µg bee venom. The patient is currently in the 3^rd year of treatment and tolerates the treatment very well.

Conclusion: Omalizumab may be used as a premedication in patients with mastocytosis who do not tolerate VIT. Although there is no consensus on the treatment protocol, treatment for 2 - 6 months is considered adequate. The long-term benefits of such treatment require further research.