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Last Updated: Sunday, 17 August, 2003, 23:05 GMT 00:05 UK
Drugs 'make asthma worse'
Child taking inhaler
Asthmatics can become oversensitive to triggers
Using too much medication may actually make asthma worse, researchers say.

Scientists believe they have discovered why common asthma treatments such as albuterol, ventolin and salbutamol can stop being effective.

All three are beta-agonist drugs, taken via an inhaler or nebuliser or as tablets, liquid or by injection, which relax the airways.

In the short-term, the drugs have an immediate effect.

A significant loss of effectiveness of treatment has not been demonstrated
Professor Martyn Partridge, National Asthma Campaign
But some studies have shown long-term daily use can make the drugs less effective.

It had been thought that this was because the body became desensitised to the effect of the drug.

But the US researchers say the body actually becomes over-sensitive to asthma triggers if the drugs are used long-term.

They say they have discovered why this can happen, and that their findings study could lead to a new way of treating asthma.

Sensitivity

Beta-antagonists bind to a receptor called beta2-adrenergic receptor (beta2AR) in lung tissue, which detects the drugs and makes them act.

Researchers from the University of Cincinnati, who looked at mice genetically engineered to either have low or high levels of beta 2AR activity.

They found long-term activation of beta 2AR also triggers high levels of an enzyme called phospholipase C- beta (PLC-beta) in smooth muscle in the lungs.

This process makes the airways highly sensitive to asthma triggers.

The research is published in the Journal of Clinical Investigation.

In an editorial in the journal, Stephanie Shore and Jeffrey Drazen from the Harvard School of Public Health and Brigham and Women's Hospital in Boston, Massachusetts, write it is possible that this is "just the tip of the iceberg".

They add that understanding the effects of beta2AR activation could lead to the development of new medications.

Professor Martyn Partridge, chief medical advisor to the National Asthma Campaign, told BBC News Online: "This is an area of considerable scientific interest, but at a clinical level.

"This should cause no concern to those with asthma as a significant loss of effectiveness of treatment has not been demonstrated in these studies."

He added: "What is important is to move the emphasis away from the need for short-acting relief medication on a regular basis and to look at controlling the condition through the use of preventative treatment."


SEE ALSO:
Asthma myth 'widely held'
13 Apr 03  |  Health
Asthma inhalers 'not suitable'
27 Feb 03  |  Scotland
Inhaler warning for asthmatics
31 Jul 02  |  Health
Asthma
15 Jun 99  |  Medical notes


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