Shares in AstraZeneca fell 1.2 percent by 0800 GMT on Friday following the news. The largest American pharmaceuticals company, whose shares gained more than 1 percent after the announcement late on Thursday, said the move was in addition to the $1.3 billion remaining on its current share buyback program. Pfizer, which has a market valuation of about $180 billion, earlier this year failed in its $118 billion bid to buy British rival AstraZeneca.