Merck & Co has received an additional approval from US regulators for its blockbuster asthma drug Singulair.

The US Food and Drug Administration has cleared Singulair (montelukast) to prevent exercise-induced bronchoconstriction (EIB), also known as exercise-induced asthma, in patients aged 15 and older and is the first and only oral tablet approved for this use. EIB is characterised by shortness of breath, coughing, wheezing and chest tightness.

In one of the studies on which the additional approval was based, patients exercised two hours, 8.5 hours, and 24 hours after taking either a single 10mg dose of Singulair or placebo. The latter demonstrated a statistically significant protective benefit against EIB when taken two hours prior to exercise and while some patients were protected from EIB at 8.5 and 24 hours after administration, some were not, Merck noted.

This new indication for Singulair will help boost its already impressive sales. The drug, which is also approved for the treatment of chronic asthma and allergic rhinitis, is Merck's top-selling product and climbed 25% to $1 billion in the first quarter. Full-year 2007 sales of the treatment will be as much as $4.2 billion, the company has forecast.

Merck applies for new use of Gardasil in EU

Meantime, Merck and partner Sanofi-Aventis have submitted an application to European regulators to expand the use for Gardasil, the world's first cervical cancer vaccine.

It is currently approved for use in girls and women aged nine to 26 against the sexually transmitted human papillomavirus but the new submission includes efficacy data showing some protection against additional cervical cancer-causing HPV types, and data on protection against vaginal and vulvar cancers.

The filing with the European Medicines Agency follows a similar submission to the US Food and Drug Administration last week.