Drug size 'key' to asthma treatment

Reliever inhalers are only 20% effective

Asthma inhalers could be made more effective if they used bigger drug particles, researchers have found.

They believe the finding could lead to less wasteful and more effective treatments for the 3.4 million people who have asthma in the UK.

The key to successful treatment is to target accurately the areas in the airways which are narrowed and inflamed.

This is an important finding since there has been little change in asthma medication and the way it is delivered over the last few decades

Dr Omar Sharif Usmani

The scientists, from the National Heart and Lung Institute, Imperial College London, have found that accuracy can be increased by altering the size of the drug particles used in "reliever" treatments.

They tested 12 asthmatic patients' response to three different particle sizes of the drug salbutamol, which is used to increase the width of the airways.

Current asthma inhalers are known to be only 20% efficient. They contain a range of particle sizes, but many do not end up where they are most needed.

There is a risk that very small particles travel so deep into the lungs that they end up in the bloodstream, where they can cause side effects.

But large particles may not even make it as far as the lungs at all.

Mapping the destination

The researchers were able to map where the particles were going by attaching a radioactive tracer.

They found that although small particles were more likely to reach the lungs, they often ended up in sites where they have little effect.

In contrast, larger sized particles ended up in the areas where they were most likely to be of use.

The researchers also found that if only larger particles were used, the dose could be reduced to just one tenth of that delivered by conventional inhalers with the same effect.

This was because fewer particles failed to reach their intended target.

They believe this could lead to the development of lower dose inhalers, which would save money and reduce the risk of side effects.

This could be particularly important with inhaled steroids if future studies show similar results in steroid particle size.

Time for change

Dr Omar Sharif Usmani, a respiratory physician at the National Heart and Lung Institute, said: "Our research shows that larger particles of bronchodilator drug achieve the greatest clinical outcome in asthma patients.

"This is an important finding since there has been little change in asthma medication and the way it is delivered over the last few decades.

"There is still a lot to be done, but this research gives us a real way forward to develop the future generation of inhalers."

Dr Usmani said the next step would be to analyse the most effective drug particle sizes for different respiratory diseases from asthma to emphysema, and for the different inhaled drugs used in these conditions.

"It is vital that we also conduct further work to see whether children, who have smaller lungs and developing airways, respond in the same way as adults to larger drug particles."