Drugmaker AstraZeneca PLC said Friday that U.S. regulators have approved a new once-daily version of its Seroquel schizophrenia drug.

Seroquel is the company's second-biggest-selling drug, with global sales of $3.4 billion last year, and analysts said approval by the U.S. Food and Drug Administration of Seroquel XR was important to extend the life cycle of the family of drugs.

The new version of the drug is under patent until 2017, while its original immediate-release formulation of the drug is facing patent challenges in the United States.

Dresdner Kleinwort said that it expects AstraZeneca to achieve a successful patient switch to the new version, but does not expect a further boost to the drug's market share.

The company has been attempting to boost its range of drugs, but suffered two recent high-profile failures of two new drugs for stroke and heart disease, which followed earlier setbacks.

AstraZeneca shares were barely changed, up just 0.1 percent at 2,748 pence ($54.15).