Investors seem pretty excited about Alexion Pharmaceuticals (NASDAQ:ALXN), which saw shares rocket up 20% after announcing fourth quarter earnings. Interestingly, the fourth quarter saw a loss of $0.10 per share due to restructuring costs (mainly from centralizing a number of its operations) and some impairment charges, although excluding these one-off charges meant the company made a profit of $0.87 per share for the fourth quarter.

However, despite making a loss including one-off charges, shares in Alexion made those gains after the release due to the company raising its own forecasts for sales of its Soliris drug. Alexion now expects more than $2 billion in annual revenue for Soliris -- considerably higher than the $1.5 billion that was delivered in 2013 and even higher than market forecasts for 2014 of $1.9 billion.

One reason for the increases in sales forecasts for Soliris is multiple marketing approvals that Alexion hopes to achieve for the drug. This process began in 2007 when Soliris was approved as an orphan treatment for a life-threatening condition called paroxysmal nocturnal hemoglobinuria, which causes a breakdown of red blood cells and can lead to organ failure. The process continued in 2011 when Soliris was approved as an orphan treatment for atypical hemolytic uremic syndrome, which can lead to kidney failure and death.

The seeking of further marketing approvals continues and just last month Soliris was approved as an orphan treatment for the prevention of delayed graft function, which can be a complication for kidney transplant patients. However, the process is unlikely to end there as Alexion looks set to continue to gain additional marketing approvals for the drug in the future.

Meanwhile, biotechnology sector peer Amgen (NASDAQ:AMGN) also delivered strong performance in its product portfolio in the fourth quarter of 2013. Although the quarter signaled the end of the profit share in Enbrel, total product sales increased by 11% versus the fourth quarter of 2012, with the combined Neulasta and Neupogen sales increasing by 8% in the fourth quarter and for the full year.

While shares did not react strongly to the release, Amgen's guidance was roughly in line with consensus forecasts and should see earnings-per-share growth in the mid-to-high single digits during 2014 and 2015.

Similarly, Gilead Sciences (NASDAQ:GILD) beat fourth quarter expectations when it posted a 4% increase in quarterly profit. However, of greater interest to the market could have been the progress on hepatitis C drug Sovaldi, which the company began marketing recently and which is expected to be a blockbuster drug.

Shares reacted favorably to the news and posted gains of around 4% immediately following the release, before falling to erase those gains. Still, shares are up 88% over the last year and, with the progress being made on marketing Sovaldi, 2014 could be an exciting year for Gilead.

Indeed, with Alexion upgrading its own forecasts for sales of Soliris, Amgen having a relatively diverse range of products that look set to deliver growth, and Gilead continuing with the process of marketing new drug Sovaldi, 2014 could be an interesting year for investors in the three companies.

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Peter Stephens has no position in any stocks mentioned. The Motley Fool recommends Gilead Sciences. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.

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