US biotechnology giant Amgen has posted mixed results for the fourth quarter which show healthy sales growth but flat earnings which were hampered by a huge hike in the firm’s R&D spend.

Revenues rose 17% to $3.84 billion, in the quarter, with net income sneaked up 1% to $833 million. The latter figure was affected by a whole host of factors not least a 52% increase in R&D expenditure to over $1 billion (including costs of a collaboration with Cytokinetics) and its $290 million cash acquisition of California-based biotechnology firm Avidia.

Sales growth was once again driven by anaemia drug Aranesp (darbepoetin alfa) which surged 27% to $1.11 billion, while Epogen (epoetin alfa) - whose growth has been pegged back by conversion of patients to Aranesp treatment - managed a 6% increase to $661 million. However this could be one of the last quarters that Amgen’s anaemia franchise performs so well, as Roche's rival erythropoietin-like drug Mircera could reach the US market by May. Amgen is suing Roche for patent infringement in a trial due to come to court in September.

Neupogen (filgrastim) and Neulasta (pegfilgrastim), used to boost white blood cells in patients on chemotherapy, saw combined sales rise 10% to $1.02 billion, but rheumatology and psoriasis treatment Enbrel (etanercept) fared less well, with sales up a modest 2% to $661 million in the face of increased competition. Colorectal cancer Vectibix (panitumumab), which was approved in September, had sales of $39 million in its first full quarter on the market, helped by the fact that Amgen priced the drug 20% lower than ImClone’s rival product Erbitux (cetuximab).

All in all a reasonable set of results, but analysts expressed concern over some setbacks in the lab. Amgen noted that Aranesp failed to show a benefit for patients in a more convenient, once-a-month formulation, while a study showed that patients taking Vectibix reported an increased incidence of diarrhoea, dehydration and infections, when they received the drug in tandem with chemotherapy and Genentech’s Avastin (bevacizumab).