Shares in Gilead Sciences rose over 6% in after-hours trading after the US firm posted strong revenue growth for the fourth quarter, boosted by royalties on sales of the flu drug Tamiflu and its HIV combo Atripla.

Net income reached $802.2 million, up 43%, while revenues rose 42% to $2.03 billion. Sales of the HIV drug Truvada (emtricitabine and tenofovir) were up 19% to $670.7 million, but were surpassed for the first time by Atripla, which combines Truvada with Bristol-Myers Squibb Co's Sustiva (efavirenz) in a single pill. Sales of Atripla leapt 50% to $697.8 million.

Viread (tenofovir) contributed $178.3 million, up 10%, driven primarily by sales of the drug as a treatment of patients with hepatitis B infection in the USA. Turnover from Letairis (ambrisentan) for pulmonary arterial hypertension increased 44% to $52.2 million.

Royalty, contract and other revenues soared to $228 million from $40.4 million in the like, year-earlier period, thanks to royalties from Roche for Tamiflu (oseltamivir). The latter, which has been sold in huge amounts since the outbreak of the swine flu pandemic, contributed $194.1 million, compared to $16 million in the fourth quarter of 2008.

On the R&D front, Gilead confirmed that it has discontinued development of the antihypertensive darusentan after it failed a Phase III study in December.