Detection of risk factors for systemic adverse reactions to SCIT with natural depot allergen extracts: a retrospective study.

BACKGROUND Some patients seem to show a particular propensity to experience systemic reactions (SR) when undergoing SCIT. This study looked at their features. METHODS 423 adults submitted to subcutaneous immunotherapy (SCIT) with 583 depot allergens extracts were studied. A "slow" build-up schedule was followed, and maintenance doses were given monthly. No mixtures of allergens were employed; multi-sensitized patients were treated with two extracts at the same time. IgE to pollen allergen components were measured. Patients experiencing several SR and those showing repeated large local reactions preventing up dosing were analyzed. RESULTS Altogether, 14% of patients experienced at least 2 SR to SCIT and further 13% repeated local reactions. All SR involved the skin. Eight treatments were stopped. No reactor was using beta-blockers. SR were not associated with pollen season, use of freshly prepared vials, administration of 2 allergens, or extract producer, nor were preceded by large local reactions. Reactors were younger than tolerant subjects (p<0.05), and females were less frequently fully tolerant than males (p<0.001). The multiple regression analysis showed that both ragweed and grass SCIT were significantly associated with adverse reactions (p<0.001). Specific IgE to Amb a 1 or Phl p 1 did not differ statistically between reactors and tolerant subjects, whereas grass pollen-allergic reactors showed higher levels of IgE to Phl p 5. Intolerance did not depend on the number of primary sensitizations or on hypersensitivity to pollen pan-allergens. CONCLUSION Young patients or women hypersensitive to grass and ragweed pollen seem at higher risk for SR during SCIT.