This finding comes as a result of a review of previous studies, with reviewers saying that older antihistamines, such as Benadryl, are more effective than new antihistamines like cetirizine (Zyrtec) or loratadine (Claritin).

“In contrast to recommendations in adults with chronic cough, antihistamines cannot be recommended as empirical therapy for children with chronic cough,” conclude reviewers led by Dr Anne Chang, a consultant in pediatric respiratory medicine at the Royal Children’s Hospital in Brisbane and the Menzies School of Health Research in Queensland.

Chang said cough is the most common symptom presented to general practitioners. A child is considered to have chronic cough after four weeks. A specific cough is associated with symptoms suggestive of an underlying problem. Non specific cough is non productive cough, without gunk, in the absence of identifiable respiratory disease. Some children with non specific cough have asthma, but most do not. Children with non specific cough are treated with a variety of therapies, including antihistamines.

In the review, five studies were examined which involved about 1,000 children, ranging from six months to 17 years old. Many children had allergies to things like grass, pollen or dust mites, or a family history of allergy.
Two larger studies described “significant improvement” both, in children who took antihistamines and those who took placebos “with no significant difference between the two groups,” the authors write. A smaller study involving 20 school-age children found that cetirizine (Zyrtec) clinically improves cough due to pollen allergy and antihistamines were found to be more effective than placebos.

In another study focussing on the use of ketotifen (Zaditen) to minimize the frequency of asthma attacks, the researchers found that they were “unable to show a therapeutic advantage of ketotifen over placebo.”
Chang said that any effectiveness the drugs have, should be weighed against their reported side effects, especially in young children, including “sedation, paradoxical excitability, dizziness, respiratory depression, hallucinations, arrhythmia and death.” However, in these studies, “Most of the events reported were minor, with irritability and gastrointestinal upset being the most common events,” stated the review.

Four children were withdrawn from one study. A dozen other children felt drowsy after taking medicine. Chang said that the small study involving Zyrtec reported “no adverse effects.”

Irwin, a professor at the University of Massachusetts Medical School, said that the older antihistamines, such as Benadryl, have more anticholinergic activity, which is to say they “dry one out” more.

“These older drugs therefore, can work when the cause of the upper airway cough is not due to allergies and they can also work if the cause of the cough is due to allergies. On the other hand, because the new drugs such as cetirizine (Zyrtec) or loratadine (Claritin) don’t have much anticholinergic activity to speak of, they will only work if the cause of the upper airway cough is due to allergies. Newer antihistamines, such as Zyrtec, “have been shown to be of help in children with allergic rhinitis. The literature supports using these specific antihistamines when children have cough in association with seasonal allergies that involve the nose,” said Irwin.
The review appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organisation that evaluates medical research.