Novartis has filed for approval of its monoclonal antibody-based drug for asthma, Xolair, in Japan, which has more than four million sufferers from the disease.

Xolair (omalizumab) was first launched onto the market in 2003, and has had a relatively slow start in the marketplace, although there are signs that its use is accelerating as clinicians become more proficient and comfortable with its use, and more countries approve the drug for sale.

Genentech, which co-developed Xolair alongside Novartis and Tanox, reported first-quarter sales rose 46% to $95 million. Novartis has rights to the drug in Europe, where it was not approved until late 2005, and has not divulged sales levels so far in 2006.

Its European debuts were in Germany and the UK in October, although there is already evidence that some health systems are balking at paying for the drug, estimated to cost around $10,000 per patient per year. Earlier this month, the Scottish Medicines Consortium decided to block treatment with Xolair on economic grounds.

Novartis has suggested that Xolair could be a billion dollar product in the USA and Europe. Japan could add upwards to $200 million a year to the peak sales tally, according to analysts.

Despite advances in therapy, approximately 20% of those with severe asthma have symptoms that remain inadequately controlled, said Novartis. And while the number of fatalities from the disease is decreasing, it is estimated that more than 3,000 people still die of asthma in Japan each year.