Standard, cluster allergen immunotherapy present similar systemic reaction risks
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There was no statistical difference in overall risk for systemic reaction between standard and cluster subcutaneous allergen immunotherapy schedules, according to a study published in Annals of Allergy, Asthma & Immunology.
However, cluster schedules may carry increased risks in the short term that additional monitoring and certain premedications can mitigate, Jonathan H. Chen, MD, of University of Maryland School of Medicine, and colleagues wrote.
The case-control study involved 91 adults with allergic rhinitis treated with standard (n = 48; mean age, 37 years; 33% men; 54% current history of asthma) or cluster (n = 43; mean age, 39 years; 46% men; 49% current history of asthma) allergy immunotherapy at the Johns Hopkins Allergy and Asthma Center between December 2021 and June 2022.
The patients in the standard immunotherapy group received approximately 26 weekly buildup injections over 6 to 9 months, whereas the cluster group received 15 buildup injections at five weekly visits.
The standard and cluster treatments both included an average of 11.1 allergens, such as pollens (78%), dust mite (64%), cat (62%) and dog (58%), with 97% of patients receiving more than one allergen.
The standard and cluster groups reached comparable protein nitrogen units (PNU; 16,626 vs. 17,488), with 83% of the standard group and 95% of the cluster group achieving their final target maintenance dose. However, the standard group showed a longer time to reach their first maintenance dose (225 days vs. 33 days; P < .001).
Total systemic reaction rates appeared comparable at 21% for the standard group and 37% for the cluster group. All these reactions occurred in the latter half of the buildup phase as percentages of target maintenance doses increased.
Based on World Allergy Organization classifications, grade 2 reactions were slightly more frequent in the cluster group, but the difference in grade distributions between the groups was not statistically significant.
Given the cluster group received approximately half the number of injections as the standard group, the rate of systemic reactions per individual injection was higher for this group despite similar overall systemic reaction rates (2.29% vs. 0.69%; incidence rate ratio = 3.3; 95% CI, 1.5-7.3).
Also, the number of systemic reactions in both groups appeared unrelated to concomitant asthma, age, total PNU target maintenance dose, number of allergens, or type of allergens included in the immunotherapy prescription.
After determining that there was a 7.4% chance of having a systemic reaction during one of the five cluster sessions, the researchers recommended that clinicians may want to monitor their patients more closely during these visits. Mitigation strategies may include vital sign recording and peak flow measurement before each injection, in addition to pretreatment with antihistamines.
Noting that the quantity of allergen in a given injection may be a primary driver of systemic reactions, considering the correlation between percent progression during the buildup phase and increasing prevalence of systemic reaction, the researchers suggested that dilution and injection volume are important factors determining increased allergen exposure compared with the number of allergens in the dose.
New studies, the researchers wrote, should use randomized design and explore how risk-mitigation strategies may benefit treatment at the most susceptible time points.
Perspective
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Michael S. Blaiss, MD, FACAAI, FAAAAI
These findings are not surprising or significant. In general, there is some evidence in the literature that accelerated immunotherapy schedules see more systemic reactions than conventional schedules, so I was not surprised by more reactions per injection in the cluster group. These results also are in line with what I have generally seen in my own experience.
Additionally, these findings suggest that patients who are starting on cluster treatment should be considered for pretreatment. We do pretreatment with rush immunotherapy, but we are not sure we need the same protocol for cluster treatment.
There is a need for a study looking at different pretreatment protocols vs. no pretreatment in cluster therapy so we can use the most effective and safe pretreatment protocol.
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