Immunotherapy with a standardized Dermatophagoides pteronyssinus extract

Abstract

Specific immunotherapy can induce severe systemic reactions (SRs), especially in patients with asthma. It also appears that potent standardized extracts may be more often involved in the generation of SRs than other extracts. Since these SRs may be potentially life threatening, it is desirable to predict their onset. A prospective study was carried out in 125 mite-allergic subjects with asthma ranging in age from 4 to 57 years to assess the incidence of SRs during a rush immunotherapy (RIT) protocol and maintenance injections and to attempt to predict the onset of the SRs. All patients received the same standardized extract of Dermatophagoides pteronyssinus with the same RIT and the same maintenance dose (3000 BU in subjects older than 10 years and 1500 BU in children younger than 10 years). Patients were carefully monitored during the RIT protocol, and possible SRs were followed for up to 2 hours after injections. Patients then received maintenance injections for a mean duration of 18.2 ± 5.6 months. During maintenance injections, patients were under supervision of a physician for 30 minutes. Within 2 weeks before the RIT, all patients older than 6 years had a pulmonary function test, skin prick test end point with the standardized D. pteronyssinus extract, and RAST. The severity of asthma was examined with the score of Aas. Forty-seven patients had an SR during the RIT protocol: four mild generalized urticaria, 35 asthma exacerbations, and eight anaphylactic shocks. None of the patients had to be admitted to an intensive care unit. Most SRs started within 15 minutes, and none of the SRs started 45 minutes or later after the last injection. The pulmonary function before immunotherapy had a predictive value for the onset of asthma, since 73.3% of patients with FEV₁ < 80% from predicted values developed asthma versus 12.6% with FEV₁ more than this threshold limit (p < 0.0001). The skin test end point was also predictive of SRs but to a lesser extent. During maintenance injections, the rate of SRs was low (4% per patient and 0.17% per injection). This study demonstrated that standardized extracts elicit a high rate of SRs in patients with asthma during RIT but that these extracts are safe during maintenance injections. Patients with severe asthma should not receive RIT with potent standardized extracts.