AstraZeneca's new boss warned on Thursday the drugmaker faced a tough year in 2013, with sales expected to fall by a mid-to-high single digit percentage rate as patent expiries continue to erode business.

Earnings will decline "significantly more than revenue" this year as operating costs rise, Britain's second biggest drugmaker said.

Chief Executive Pascal Soriot hopes eventually to turn the group around by investing in existing growth areas like emerging markets, diabetes care and the new heart drug Brilinta. He is also weighing the case for acquisitions.

Soriot, who joined from Roche in October, will set out his strategy in detail during a keenly awaited investor day on March 21.

In a bid to clear the decks and give himself a free hand to set future direction, Soriot said he wad withdrawn mid-term planning assumptions for revenue and profit margin set by previous management.

Sales in the fourth quarter of 2012 fell 16% to $7.28 billion, generating "core" earnings, which exclude certain items, down 3% at $1.56 a share. The slower decline in earnings reflected lower costs in the quarter and a favourable tax adjustment.

Industry analysts, on average, had forecast sales in the quarter of $7.20 billion and earnings of $1.35 a share, according to Thomson Reuters I/B/E/S.

Faced with loss of exclusivity on once best-selling medicines and a thin pipeline of new drugs, Soriot needs to consider some bold moves to get AstraZeneca back on its feet.

But he has to tread carefully on new investment if he is to avoid disappointing investors who own the stock as an income play, given its near 6% dividend yield.

His decision to suspend share buybacks on his first day in the job four months ago immediately prompted speculation that he might embark on sizeable acquisitions.

Big hits to come

AstraZeneca is not alone in facing big patent losses, but while rivals like GlaxoSmithKline and Sanofi are over the worst, AstraZeneca's biggest losses are still to come, with Nexium for stomach acid and cholesterol fighter Crestor losing U.S. protection in 2014 and 2016.

As a pure pharmaceuticals group, without the cushion of alternative revenue streams found at more diversified rivals, AstraZeneca is particularly exposed to patent losses on its key prescription drugs.

Short-term wins from the company's new drug pipeline look unlikely, with expectations for experimental rheumatoid arthritis drug fostamatinib dwindling after disappointing clinical trial results last month.

One established medicine that may surprise on the upside is diabetes drug Onglyza, which is marketed with Bristol-Myers Squibb and could potentially show a heart benefit in a clinical study that will report later this year.

AstraZeneca shares have gained ground in recent months but the stock remains the laggard of the global pharmaceutical sector, trading on around 8.6 times expected earnings, a 30% discount to large British rival GSK.