Background Allergen-specific immunotherapy (SIT) is an effective treatment for patients with respiratory allergies. However, subcutaneous injection of allergens can provoke systemic side-effects.
Objective This study was carried out to determine the incidence and risk factors of systemic reactions caused by SIT treatment, using extracts of different inhalant allergens, adsorbed in aluminium hydroxide and biologically standardized with the major allergens quantified in mass units.
Methods Five hundred and fifty-five subjects with allergic rhinitis and/or asthma were evaluated on clinical history and skin prick test (SPT) reactions to common inhalant allergens. Subcutaneous SIT was administered to all patients, according to the suggested precautionary guidelines and administration schedule. Patients were treated with house dust mite, grass pollen, Parietaria judaica pollen and olive pollen extracts, each receiving one or two extracts.
Results A total of 36 359 injections were administered in the 555 patients. We observed 34 episodes of serious systemic side-effects (0.093% of all injections), in 29 patients (5.2% of all patients), and no fatalities. About 55% of patients reported mild rhinitis and asthma. The majority (59%) of the serious systemic reactions (SSR), and all the anaphylactic reactions, were immediate (i.e. occurred within 30 min after the injection). Asthmatic subjects were at higher risk of SSR than patients with rhinitis (P = 0.01). Most of the side-effects observed occurred during the dose-increase phase (P < 0.05). There was no association of SSR with age, gender, SPT reactivity or allergen type.
Conclusion SIT performed in patients with respiratory allergies by specialized staff with the allergen extracts studied, standardized in mass units, provoked a low rate of SSR. The significant risk factors for systemic reactions were asthma and the build-up period.