A mist inhaler used to improve breathing in people with lung diseases including chronic bronchitis and emphysema may increase their risk of dying by 52 per cent, US and British researchers said.

The increased risk occurred in patients who used the Spiriva Respimat inhaler, a newer device sold by privately held Boehringer Ingelheim (BI) and Pfizer . It delivers a soluble form of Spiriva, known generically as tiotropium.

The inhaler is used to treat chronic obstructive pulmonary disease, or COPD, the fourth-leading cause of death worldwide, which includes the chronic lung diseases emphysema and bronchitis. COPD is usually due to decades of smoking.

"What we think is going on is that the mist inhaler is delivering a higher concentration of tiotropium than it should be and that may be increasing the risk of death," Dr Sonal Singh of Johns Hopkins University School of Medicine, who led the study, said in a statement.

The inhaler is approved for use in Britain and Europe, but failed to win a nod from the US Food and Drug Administration, which noted an excess number of deaths in a study of 17,000 patients. Instead, the FDA said it wanted more proof the inhaler was safe.

The new study, published in the British Medical Journal, is based on an analysis of data from five clinical trials involving 6,500 people.

It found that the risk of death in patients using the tiotropium Respimat inhaler was 52 percent higher than patients who used a placebo. "We estimate that there will be one additional death for every 124 patients treated for a year with tiotropium Respimat," Dr Yoon Loke of Norwich Medical School at the University of East Anglia, who worked on the study, said in a statement.

He said some of the added risk stems from patients dying of heart trouble, especially for those with existing heart problems that may be made worse with use of the product.

Pfizer and BI said in a statement they were aware of the article and were in the process of reviewing it, adding that all the studies included in the pooled analysis had been published and already shared with European regulatory authorities.     

Savvas Neophytou, an analyst at Panmure Gordon, said the possible negative impact on sales as a result of the report could benefit GlaxoSmithKline's rival product Advair.     

That might offset the looming threat of generic competition to Advair in non-US markets, Neophytou added. A copycat version of Advair was recently approved in Sweden.

Most COPD sufferers use inhalers to help them breathe and more than half a million prescriptions for tiotropium inhalers were issued in Britain last year. - Reuters