Updated from 3:06 p.m. EDT

Shares of Merit Medical Systems ( MMSI) were among the worst-performing health and pharmaceutical stocks Wednesday, falling 15% after the company warned that third-quarter earnings and sales would fall below Wall Street expectations.

The maker of disposable medical products expects earnings of 14 cents to 15 cents a share on sales of $35 million to $36 million. Analysts polled by Thomson First Call had been expecting earnings of 19 cents a share on sales of $39.1 million. The company said the shortfall in earnings and sales was caused by reduced demand for its products during the quarter, which it attributed to an increase in competition, fewer procedures being conducted using its products, and -- to a lesser extent -- weather-related disturbances in the southeastern United States. Shares traded down $2.14 to $12.05.

Cell Genesys ( CEGE) fell 12.8% after the biotechnology company released preliminary third-quarter results and said it would sell $100 million in convertible notes. The company expects to post a third-quarter loss of 52 cents a share on sales of $3.2 million. Analysts had been expecting a loss of 52 cents a share on sales of $3.25 million. As for the convertible debt offering, the company said it plans to use the proceeds to repay two outstanding loans totaling $95 million. The debt repayment will eliminate restrictions on the company's $60 million cash balance. Shares traded down $1.09 to $7.42.

Shares of aaiPharma ( AAII) rose 0.5% after the company announced its lenders waived compliance for certain covenants in the company's senior secured credit facility. The waiver covers the quarters ending Sept. 30 and Dec. 31, respectively, and is contingent upon the company meeting minimum EBITDA thresholds. Earlier this month, the company missed an interest payment of $10 million on its 11.5% senior subordinated notes due 2010. Shares traded up 1 cent to $1.95.

AtheroGenics ( AGIX) fell 8.2% after the company said its arthritis drug failed a phase II clinical trial. The results showed that none of the drug's three dosages showed a statistically significant improvement when compared to a placebo. As a result, the company is discontinuing clinical trials of the drug for use in rheumatoid arthritis. Shares traded down $2.38 to $26.56.

Other health care volume movers included Pfizer ( PFE), down 31 cents to $29.55; Merck ( MRK), down 78 cents to $30.07; Lincare Holdings ( LNCR), up $5.68 to $36.99; Amgen ( AMGN), down 68 cents to $54.99; Schering-Plough ( SGP), down 38 cents to $17.41; and Genentech ( DNA), down $1.25 to $46.95.

More from Stocks

Week Ahead: Trade Fears and Stress Tests Signal More Volatility To Come

Week Ahead: Trade Fears and Stress Tests Signal More Volatility To Come

3 Great Stock Market Sectors Millennials Should Invest In

3 Great Stock Market Sectors Millennials Should Invest In

Why Millennials Are Ditching Stocks for ETFs

Why Millennials Are Ditching Stocks for ETFs

Trump's 'Space Force' Could Launch a $1 Trillion Industry, Morgan Stanley Says

Trump's 'Space Force' Could Launch a $1 Trillion Industry, Morgan Stanley Says

Abiomed Stock Should Rise Some 12% From Here, Piper Jaffray Analyst Says

Abiomed Stock Should Rise Some 12% From Here, Piper Jaffray Analyst Says