Isis Pharmaceuticals Inc.’s stock dropped nearly 10 percent following the announcement of its fourth quarter earnings, despite more than doubling its revenue for the quarter ended Dec. 31, 2013. The company’s net loss increased significantly, however.

Shares for Isis (Nasdaq: ISIS) closed at $51 on Feb. 28 — down $5.37 from the previous day of trading.

For the quarter, Isis’ revenue was $42.2 million, compared with $19.9 million in the like quarter of 2012. Net loss grew to $24.3 million in the fourth quarter of 2013, compared with $2.6 million in the fourth quarter of 2012. This is largely due to a rise in research and development spending, which rose 34 percent to $57.4 million, because Isis’ pipeline of drugs “matured substantially” and many are in the midst of later-stage clinical trials, CEO Stanley Crooke said in a statement.

Isis has a lot of cash on hand, — ending the year with $656.8 million in cash, cash equivalents and short-term investments. It ended 2012 with $374.4 million. This increase comes from a $225 million cash influx from its drug development partners, and the $236 million it raised in a secondary stock offering.

The company, which is still not profitable, projects it will end 2014 with $575 million in cash, but by then it plans to have three drugs in phase 3 trials and 10 in phase 2 trials.