First-generation antihistamines increase delirium risk in older hospitalized patients

An analysis in the Journal of the American Geriatrics Society reveals that older inpatients admitted to physicians who prescribe higher amounts of first-generation antihistamines face an elevated risk of delirium while in the hospital.

First-generation antihistamines, such as diphenhydramine (Benadryl), are among the leading causes of medication-related harms in older adults, and although these medications are indicated for histamine-related conditions such as hives and anaphylaxis, they may be prescribed inappropriately.

When investigators analyzed data on 328,140 patients aged 65 years and older who were admitted by 755 attending physicians to 17 hospitals in Ontario, Canada in 2015–2022, they found that the overall prevalence of delirium was 34.8%. Patients admitted to physicians who more commonly prescribed first-generation antihistamines had 41% increased odds of experiencing delirium compared with patients admitted to physicians who rarely prescribed first-generation antihistamines.

We hope our study raises awareness among hospitalists that sedating antihistamines can be harmful, and should be prescribed with caution."

Aaron M. Drucker, MD, corresponding author, University of Toronto and Women's College Hospital