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H1 antihistamines and dementia risk in allergic rhinitis

Published: June 25, 2024

Antihistamines are commonly used to alleviate symptoms of allergic rhinitis, a condition affecting a large portion of the population. These medications are classified into first-generation (FGAs) and second-generation (SGAs) H1 antihistamines based on their pharmacokinetic properties and side effects. FGAs, known for their strong anticholinergic effects, can cross the blood-brain barrier and are linked to sedation and cognitive impairment. SGAs are less likely to cross the blood-brain barrier and have milder side effects. Given the potential cognitive risks associated with long-term antihistamine use, this study explores the relationship between cumulative antihistamine use and the risk of developing dementia in patients with allergic rhinitis.

In a recent study published in The Journal of Allergy and Clinical Immunology: In Practice, Su et al. conducted a retrospective cohort study using data from Taiwan’s National Health Insurance Research Database from 2011 to 2017. The study included 714,052 patients with new-onset allergic rhinitis, categorized into those using FGAs or SGAs (677,971 patients) and nonusers (36,081 patients). Antihistamine use was quantified using cumulative defined daily doses (cDDD), and patients were grouped into nonuser, less than 60 cDDD, 60 to 120 cDDD, and more than 120 cDDD categories. The primary outcome was the incidence of dementia, assessed using a Cox proportional hazard model, with adjustments for demographic characteristics and comorbidities.

The study found a dose-dependent increase in dementia risk among antihistamine users. For FGA users, the adjusted hazard ratios for dementia were 1.13, 1.29, and 1.51 for less than 60 cDDD, 60 to 120 cDDD, and more than 120 cDDD, respectively. SGA users also exhibited increased dementia risk, with adjusted hazard ratios of 1.11, 1.19, and 1.26 for the same cDDD categories. FGAs were associated with a higher dementia risk compared to SGAs. These findings suggest that both FGAs and SGAs pose a risk for dementia, which escalates with cumulative dosage. The study highlights the importance for clinicians to consider these risks when prescribing antihistamines, especially for long-term use.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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