GlaxoSmithKline's best-selling asthma drug Advair is proving tough to copy by generic rivals, the Wall Street Journal reports.

That challenge could allow GSK, the British drug maker with its North American headquarters in Research Triangle Park, to protect Advair even after its loses patent protection next year.

Typically, losing such protection opens the door for cheaper copycat versions and hurts sales. But Advair combines two drugs in a fine powder that's inhaled through an intricate device called a Diskus.

Generic-drug makers Teva Pharmececeutical and Sandoz, a subsidiary of Novartis, have each recruited GSK to help develop a generic rival, the newspaper reports. The difficulty represents a challenge for generics companies, trying to replicate increasingly complex drugs.

GlaxoSmithKline said today that more than 25,000 Advair inhalers had been stolen from a warehouse in Richmond, Va.

The inhalers, which contain medication used by asthma sufferers, were taken from a distribution facility on Aug. 2 before they could be shipped out to pharmacies.

The company is advising that the medicine could present a health risk since it had been removed from the legitimate supply chain and optimum storage conditions.

Patients with Chronic Obstructive Pulmonary Disease had an increased risk of pneumonia if they were long-time users of popular corticosteriod inhalers.

Those findings were published Monday in the Archives of Internal Medicine by researchers at Wake Forest School of Medicine.

The reseachers examined 18 clinical trials involving more than 17,000 patients to explore links between pneumonia and the inhalers, including Advair and Symbicort.

According to their analysis, patients who used the inhalers for at least 24 weeks had a 60 percent to 70 percent increased risk of developing pneumonia.

The inhalers are not approved by the government as a sole therapy for COPD, a respiratory ailment that causes wheezing and shortness of breath. But they can be prescribed with other drugs that dilate the lungs.

"Given the substantial emerging risk of pneumonia and its associated morbidity and mortality in patients with chronic obstructive lung disease, and the uncertain benefit of adding an inhaled corticosteroid to a long-acting bronchodilator, clinicians should re-evaluate the benefit-harm profile of long-term inhaled corticosteroid use among patients with COPD,” Dr. Sonal Singh, an assistant professor of internal medicine and lead investigator for the study, said in a prepared statement.