Shares of Amgen Inc. fell 6 percent in after-hours trading Tuesday after the biotech giant reported first-quarter sales that fell short of Wall Street expectations.

After the markets closed, the Thousand Oaks company reported net income of $1.43 billion ($1.88 a share), 21 percent higher than in the same period a year earlier.

The company got a boost from $13 million in federal and state tax benefits during the quarter. Adjusting for one-time expenses, the company earned $1.96 a share, better than the $1.84 adjusted profit expected by analysts surveyed by Thomson Reuters.

Revenue rose 5 percent to $4.24 billion, lower than the Wall Street consensus of $4.37 billion. Growth was led by the company’s Enbrel treatment for psoriasis and rheumatoid arthritis and its Prolia drug for osteoporosis, but sales continued to falter for its anemia drugs Aranesp and Epogen.

Shares earlier closed down 66 cents, or less than 1 percent, to $112.76 on the Nasdaq then slipped 6 percent in after-hours trading.