US stocks fell at the open, as global uncertainty persisted and a further fall in oil prices upset investors.
The broad S&P500 index was down 0.5% at 2,026, while the S&P Midcap 400 was down 0.6% at 1,403 and the S&P Smallcap 600 was down 0.4% at 661.
The biggest fallers among mid-caps was United Therapeutic (NASDAQ:UTHR), down 9.16% to $110.46, and among the top five was Community Health Systems (NYSE:CYH), down 5.4% to $16.82. Traders said there was no fresh news on the two stocks but a pullback was cited after gains earlier in the week.
The small cap declines were led by Lannett Co (NYSE:LCI), down 13% to $17.72, after the company lowered its 2016 guidance and was downgraded to "sell" from "buy" by Canaccord Genuity.
On Wednesday, the Philadelphia-based pharmaceutical products company projected 2016 revenue to range between $555mln to $565mln. Previously,
Lannett projected 2016 revenue to range between $585mln to $595mln.
Lannett lowered its revenue guidance due to softness in the generic drug market and product launch delays, the company said in a statement.
The US benchmark West Texas Intermediate was down 1.4% at $39.23 and heading for its first weekly decline since the middle of February.
Downbeat oil prices came on the back of news on Wednesday that US stockpiles have increased by 9.36mln barrels to 532.5mln - the highest level since 1930 and three times the rise forecast - official data showed yesterday, fueling the glut worry.
Among the big losers on Thursday was Portola Pharmaceuticals Inc (NASDAQ:PTLA), which lost over 27% to stand at US$20.86 after it announced top line phase III study data which missed the main efficacy testing threshold.