People with asthma who regularly use long-acting beta agonist inhalers may find that they have a delayed response when they need to use a short-acting “rescue” inhaler for asthma flare-ups, a UK study shows.

When inhaled, beta agonist drugs dilate the constricted airways of people with asthma. Patients are often prescribed long-acting forms of the drugs such formoterol or salmeterol in combination with inhaled steroids to control their condition. Seretide and Symbicort are examples of such combination inhalers.

However, the new findings suggest that the response to the short-acting beta agonist salbutamol (also known as albuterol), used for an acute asthma attack, may be blunted following treatment with combination inhalers.

“Clinicians prescribing these combination inhalers need to warn their patients that they may need to use more salbutamol if they have an acute attack,” study leader Dr. Brian J Lipworth from the University of Dundee, Scotland, told Reuters Health.

There has been a suspicion that the development of tolerance to beta agonists might depend on an individual patient’s genetic make-up, as it relates to the genotype of beta receptors. However, that doesn’t seem to be the case.

As they report in the medical journal Thorax, Lipworth and colleagues investigated 20 patients either of the two types of beta-receptor genes. The subjects were tested for their response to salbutamol after an induced asthma attack, before and after they had used Seretide or Symbicort inhalers for two weeks.

After using either combination inhalers, recovery from the asthma attack with salbutamol was significantly delayed to a similar degree in both genetic types, “due to cross tolerance induced by formoterol and salmeterol,” the researchers report.

Commenting on these findings, Lipworth noted that “as combination inhalers are being used more and more as first line therapy, prescribers need to be aware that the acute rescue response to salbutamol may be blunted with delayed recovery in the setting of acute asthma.”