Administration-related reactions following first-dose subcutaneous daratumumab to inform implementation of a 30-minute observation period

IntroductionSubcutaneous daratumumab has lower rates of administration-related reactions (ARRs) than intravenous daratumumab and shorter administration times. However, the optimal monitoring following the first dose remains uncertain and varies across institutions. This medication use evaluation assessed first-dose ARRs under a 2-h observation protocol and whether available findings support reduced 30-min observation.MethodsThis retrospective, single-center cohort study included patients who received first-dose subcutaneous daratumumab at the Zuckerberg Cancer Center between March 6, 2024, and July 31, 2025. The primary endpoint was ARR incidence. Secondary endpoints included time to onset, CTCAE version 6.0 severity, and management interventions. Premedication adherence and potential chair-time savings from reducing observation from 4 to 2 h were also evaluated. After implementation of the 30-min observation period, 26 additional patients treated from April through June 2026 were reviewed for ARRs.ResultsAmong 50 patients in the primary cohort, one experienced an ARR (2%). Grade 3 ARR occurred 150 min after administration and required intravenous methylprednisolone, diphenhydramine, famotidine, and intramuscular epinephrine. Premedication deviations included diphenhydramine 25 mg instead of 50 mg and omitted montelukast. The patient tolerated subsequent doses after receiving the complete regimen. No ARRs occurred among the 26 patients evaluated after implementation of 30-min observation.ConclusionFirst-dose subcutaneous daratumumab was associated with a low ARR incidence, with the only reaction occurring beyond 2 h. Together with published evidence and institutional experience, these findings supported implementation of 30-min observation, with no ARRs observed after implementation. Larger studies with longer follow-up are warranted to further assess abbreviated observation.