Time to take sedative antihistamines off menu

Newer, less-sedating antihistamines have very few adverse effects

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There is little role for sedating antihistamines in the management of allergic conditions, according to Australian experts who say their potential harms make them a poorer choice compared with the newer drugs. 

Less sedating antihistamines, such as the second-generation drug loratadine and third-generation drug desloratadine, have a better safety profile for use over the long term compared with sedating drugs such as promethazine. 

Writing in Australian Prescriber, Canberra immunologists Associate Professor Katrina Randall and Dr Carolyn Hawkins warned clinicians to stay away from sedating antihistamines, saying they now have “little role” in therapeutics. 

“Sedating antihistamines interfere with rapid eye movement sleep and have been associated with poorer school performance in children with allergic rhinitis, aviation and car accidents, and anticholinergic effects in older patients such as urinary retention and delirium,” Professor Randall said. 

Promethazine and other injectable antihistamines have also been linked to a greater risk of severe tissue injury, such as gangrene. 

The risks of side-effects associated with the first-generation drugs was enough to prompt the Global Allergy and Asthma European Network to call for a prescription-only restriction, the authors noted. 

“The main role for sedating antihistamines is in pregnancy, where they can be used for any of the common indications for antihistamines, as they have the strongest evidence of safety,” they added. 

Their long history of use among pregnant women can provide clinicians with more confidence in their safety than the shorter, but still positive, evidence base supporting the safety of the newer antihistamines. 

However, the authors did urge clinicians to warn pregnant women about potential risks such as sedation and risks around driving while taking the older-type medication. 

On the other hand, the newer and less-sedating antihistamines had “very few adverse effects”, Professor Randall and Dr Hawkins said. 

The less-sedating antihistamines in Australia included cetirizine, desloratadine, fexofenadine and loratadine. 

“Cetirizine is the one most likely to cause sedation, particularly in higher doses. Although very rare, idiosyncratic hypersensitivity reactions have been described for each of the antihistamines.”

Headache, fatigue, drowsiness, insomnia and rash are also associated with their use.

The paper also noted that sedating antihistamines had been associated with a lowered seizure threshold. 

The most-sedating antihistamines available in Australia include cyproheptadine, dexchlorpheniramine, pheniramine, promethazine and trimeprazine. 

The authors concluded that the older antihistamines “have now been superseded by newer, less-sedating drugs”.