Double-digit gains in both sales and earnings at Amgen in the third quarter have prompted the US biotech to raise its yearly guidance yet again, despite a hefty increase in research spending.

Sales rose a healthy 15% to $3.61 billion, driven by anaemia drug Aranesp (darbepoetin alfa) which surged 27% to $1.07 billion in the quarter, with net income up 14% to $1.1 billion, even though R&D spending rose 49% to $835 million.

Aranesp’s parent drug Epogen (epoetin alfa) – whose growth has been pegged back by conversion of patients to Aranesp treatment - also managed a 6% rise in sales to $633 million, which gave a rosy glow to the company’s anaemia franchise, although a black cloud is lurking on the horizon in the shape of Roche’s rival erythropoietin-like drug Mircera, which could be on the US market as early as next February.

Amgen is suing Roche for patent infringement in a trial due to come to court in September next year. And it has also signed a deal with Fresenius, the largest supplier of dialysis in the USA, to act as sole supplier of erythropoietin products for a period of five years, closing Roche out of that portion of the market.

Neupogen and Neulasta, used to boost white blood cells in patients on chemotherapy, saw sales rise 13% to $998 million, but rheumatology and psoriasis treatment Enbrel (etanercept) fared less well, with sales up a modest 6% to $705 million in the face of increased competition in the marketplace from other drugs that work by blocking the activity of tumour necrosis factor, such as Abbott’s Humira (adalimumab).

The hike in research costs is a result of the large number of projects in Amgen’s late-stage pipeline, said the company, which mean that it has nine large-scale trials ongoing. R&D spend should grow at a lower margin next quarter, said Amgen.

Amgen raised its 2006 forecast to include earnings per share of $3.85-$3.95, up from $3.75-$3.85 when it presented second-quarter results.