Hamilton, Ontario—Spring allergy season is coming on with a vengeance in much of North America, and a new review provides some advice on optimal use of antihistamines.

Pharmacists might not realize that many allergy sufferers are using those medications incorrectly, according to the report.

“People need to rethink what they stock in their home cabinets as allergy medicines, what hospitals keep on formulary, and what policymakers recommend. The message needs to get out. This publication is on time for the spring allergy season and as COVID vaccines roll out, for which rashes are common and antihistamines can be helpful,” said lead author Derek Chu, MD, PhD, of McMaster University.

In a review on the topic, published in the Canadian Medical Association Journal, coauthor Gordon Sussman, MD, of the University of Toronto’s Temerty Faculty of Medicine, advised, “There are new, modern, second generation antihistamines that are potent, specific, fast acting and of proven safety which everyone should be using to treat allergic rhinitis and hives.”

The article points out that antihistamines are among the most commonly and incorrectly used medicines worldwide. The authors emphasize that, while antihistamines are valuable to relieve symptoms of hay fever and outbreaks of hives, they should not be used for asthma, eczema, coughs, or insomnia.

The authors add that first-generation antihistamines, such as diphenhydramine, chlorpheniramine, or hydroxyzine, can be associated with substantial and sometimes fatal side effects. They affect cognitive functions and overdosing can occur, they note.

“Overdose can result in death from anticholinergic and anti-alpha-adrenergic effects, and QT prolongation (including torsades de pointes). First-generation antihistamines are on the Beers list of potentially inappropriate medications for older persons,” according to the review.

On the other hand, according to the article, newer antihistamines are safer, as affordable, and as effective as first-generation antihistamines. Furthermore, the authors write that later-generation antihistamines are proven to be more effective and last longer with fewer side effects, such as drowsiness.

“Compared with first-generation antihistamines, systematic reviews of randomized controlled trials have found newer antihistamines to be safer (e.g., 4% sedation vs. 28%), longer lasting (12–24 h vs. 4–6 h dosing) and faster acting (50 vs. 80 min),” the authors advise. “The World Health Organization replaced chlorpheniramine with loratadine on its essential medicines list in 2013 for these reasons for preferred antihistamines.”

The review team notes that bilastine and fexofenadine are the least-sedating options but add that neither those nor any antihistamine should be consumed with alcohol.

The authors caution about the dangers of using antihistamines instead of epinephrine to treat anaphylaxis, adding that oral drugs can be used together with epinephrine injections to treat anaphylactic reactions, but they are not a substitute. “Intravenous diphenhydramine can cause vasodilation and sedation, which can worsen hypotension and confound assessment of patients with anaphylaxis,” according to the article.

The review also answers a question often posed to pharmacists. It states that most antihistamines are safe to use during pregnancy and breastfeeding, adding that research has shown that antihistamines at standard doses do not harm fetuses during pregnancy and may be used during breastfeeding.

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