Methods: We performed a five-year retrospective chart review of all patients who underwent single-blinded placebo-controlled two-step challenges to beta-lactams in an outpatient setting.
Results: Between 2010 and 2015, 154 patients underwent 162 challenges to beta-lactams. The majority of patients was female (81.2%) with a mean age of 51.4 years (SE ±1.5). All challenges were preceded by negative skin testing and most (98%) were preceded by placebo. Reactions to placebo occurred in 11.3% of challenges (n=18) and to beta-lactams in 6.2% (n=10). Patients who reacted to placebos were female (100%, p=0.04) and more likely to have a history of multiple reported drug allergies: 4.6 (SE ±0.9) vs. 2.5 (SE ±0.5) drug allergies in those who reacted to medication (SE ±0.5) vs. 2.4 (SE ±0.1) drug allergies in those who had no reaction (p<0.01). The majority of all reactions was mild and subjective (n=24/28, 86%) with spontaneous resolution (n= 25/28, 89%). Reactions to placebos included pruritus (n=12), sensation of throat tightness (n=2), and hives (n=1). Reactions to medications included pruritus (n=4), tingling (n=3), and fatigue (n=3). No anaphylactic reactions occurred.
Conclusions: This study validates the safety of two-step challenges to beta-lactams. Since a greater number of reactions occurred to placebo rather than to beta-lactams, it is likely that some reactions are not due to drugs.