Amgen’s fourth-quarter adjusted earnings have edged up 3%, but revenues were flat, dampened by lower-than-expected sales of its flagship anaemia drug Aranesp.

Net income reached $1.12 billion, while revenues came in at $3.75 billion, as sales of Aranesp (darbepoetin alfa) fell 15% to $706 million. The decline was principally due reimbursement problems the firm has faced, while sales of the older erythropoiesis stimulating agent, Epogen (epoetin alfa) were up 1% at $646 million.

Combined worldwide turnover of Amgen’s white blood cell stimulators Neulasta (pegfilgrastim) and Neupogen (filgrastim) climbed 6% to $1.18 billion. North American sales of the anti-inflammatory Enbrel (etanercept) were up 7% to $913 million, while global revenues for Sensipar (cinacalcet), for the treatment of secondary hyperparathyroidism in dialysis patients, leapt 20% to $153 million. Sales of the anticancer antibody Vectibix (panitumumab) were up 39.4% at $46 million.

Amgen said that full-year 2009 earnings, excluding items, should be in the region of $4.55-$4.75 per share on revenues of $14.8-$15.2 billion, a forecast that was seen by analysts as being on the light side. Observers are now waiting to see what happens with denosumab, the company’s eagerly-anticipated investigational osteoporosis treatment which was filed with US regulators at the end of last year.

Amgen believes that the drug has the potential to be a blockbuster and Cowen & Co analyst Eric Schmidt said that clinical data on denosumab is more important to Amgen’s stock price than the financials at the moment.