A Randomized, Double-Blind, Placebo-Controlled Study of Omalizumab for Idiopathic Anaphylaxis

Study Summary

Background: * Omalizumab is an approved drug for the treatment of asthma by the Food and Drug Administration. * Researchers are now studying this drug in a double-blind placebo-controlled manner to assess efficacy in patients with idiopathic anaphylaxis (recurrent hypersensitive allergic episodes for which a cause is not identified). * The study will improve understanding of the mechanisms involved in anaphylactic reactions as a response to the downregulation (a decrease in the number of receptors on the surface of cells) in mast cell (a resident cell with several types of tissues) activation, and lead to the development of strategies to better prevent or treat anaphylaxis. Objectives: * To determine whether treatment with omalizumab will reduce or prevent episodes of unprovoked anaphylaxis (an acute allergic reaction) in subjects with a history of idiopathic anaphylaxis. * To assess pharmacodynamics (physiological effects of a drug) and identify patients with undiagnosed mastocytosis (rare disorders caused by too many mast cells). * To investigate cellular and molecular mechanisms of signaling and the effect of omalizumab on mast cells or basophils (a cell in the leukocyte family that releases histamine, which affects allergic response) and explore other regulatory pathways that may be involved with modulation of mast cell degranulation. Eligibility: * Patients between 18 and 70 years of age who have been diagnosed with idiopathic anaphylaxis, a diagnosis that is made only after other causes of anaphylaxis have been considered. * Patients with documented anaphylaxis episodes (mild to severe) at least six times within the past 1 year period, at least once within the last 4 months, and with at least one of the following: * Elevated serum tryptase above baseline within 2 hours of the event. * Emergency room visit with documented anaphylaxis without a known cause established by the acute onset of an illness (minutes to several hours) with involvement of the s

Primary Outcome

To determine if treatment with omalizumab over 6 months will produce a reduction in the number and timing of anaphylactic events in subjects with a history of frequent idiopathic anaphylaxis. Ordinal outcome of participants based on number of events in 6 months after baseline and timing of first event. Events were calculated based on detailed event logs maintained by the patients and collected every 2-4 weeks based on injection schedule. Mean percent change in number of events experienced while

Interventions

• DRUG Epinephrine
• DRUG Placebos
• DRUG Omalizumab (Xolair)