British experts have expressed concerns that some patients may be genetically predisposed to react badly to long-acting beta-agonists (LABAs). Last year, the US Food and Drugs Administration issued a health warning about the drugs, saying doctors should only prescribe them if other medication had failed to control attacks.

LABAs work by opening up the airways over a long period of time and include inhalers such as Serevent, Oxis and Foradil. Studies in the US have indicated that some patients' conditions were significantly worsened, and some deaths had occurred, as a result of using this form of medication.

However, Frances Byrne of the Asthma Society of Ireland said Irish patients should not be unduly worried by the research, which is still ongoing.

"In Ireland, LABAs are prescribed only as an add-on medication and never on their own, " she said. "In the US, they were prescribed without preventative therapy, which doesn't happen over here. They are only used for maintaining a good balance of health and never in emergency care."

LABAs are licensed in Ireland for adults and children from the ages of five and over.

Doctors tend to prescribe them only in severe cases of asthma, where relief inhalers are failing to control symptoms on their own.

"All medication has implications, and GPs and parents should continuously assess and monitor how it is working for the individual and whether it is suitable, " said Byrne. "It needs to be remembered that the danger of discontinuing asthma medication far outweighs the danger of possible side effects." Some 470,000 Irish people have asthma.