The effects of repeat omalizumab administration on skin test positivity and the assessment of the safety of administration in patients with positive skin tests to mouse antigen.

Patients receiving omalizumab for moderate-to-severe allergic asthma were evaluated for the effect of omalizumab administration on immediate hypersensitivity skin test reactions. The existence of a relationship between a positive skin test for mouse antigen and risk for anaphylaxis in patients receiving omalizumab was also investigated. Seventeen patients were skin tested serially to tree, grass, and weed pollens; molds; dust mites; cat and dog allergens; mouse antigen; and cockroaches. Skin tests were performed before the initiation of omalizumab therapy and at each subsequent clinic visit (every 2-4 weeks). At the time of each visit, skin tests were performed immediately before the subcutaneous administration of omalizumab and 20 minutes afterward. A marked reduction in skin test reactivity was noted after the administration of omalizumab. Some of these reductions became more pronounced 20 minutes after administration compared with testing done before administration. There was one mild urticarial reaction 20 minutes after administration in a patient with a positive skin test to mouse antigen. The skin test was positive at the time of this reaction. Omalizumab therapy was continued without further adverse events and the skin test to mouse antigen became negative. In addition, seven other subjects with positive skin tests to mouse antigen have received repeated doses of omalizumab without adverse events. Omalizumab administration results in significant reduction of skin test reactivity to aeroallergens. Furthermore, a positive skin test to mouse antigen does not automatically preclude the use of omalizumab for therapy of moderate-to-severe allergic asthma.