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Drugs 'make asthma worse'

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, Shore and 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. "