AstraZeneca has filed for approval of a long-acting formulation of its schizophrenia drug Seroquel in Europe and Canada, following on from an earlier submission in the USA in July.

Seroquel SR (quetiapine fumarate) will be dosed once-a-day, rather than twice-daily for the currently marketed version, and in addition will have the benefit of achieving a therapeutically-effective dose by the second day of treatment, theoretically speeding up the response to treatment.

But as well as the benefits for patients and doctors, Seroquel SR also plays a pivotal part in shoring up AstraZeneca’s Seroquel franchise, which is facing generic competition in the USA from Teva Pharmaceutical Industries.

Sales of Seroquel reached $1.66 billion in the first half of 2006, a 27% rise year-on-year, and is AstraZeneca’s second biggest-selling product behind gastrointestinal Nexium (esomeprazole). The new formulation has patent protection out to 2017, according to the drugmaker, which will try to migrate patients from the current formulation of to the new one in order to mitigate the impact of generic competition.

Seroquel’s current formulation has patent protection out to 2011, according to AstraZeneca, but could face competition from Teva in 2008 – or even earlier depending on the course of ongoing litigation between the companies.