Shares of Sonus Pharmaceuticals ( SNUS) were among the best-performing health-related stocks Friday, rising 9% after the drug developer posted a narrower-than-expected fourth-quarter loss.

The company reported a loss of $3.3 million, or 11 cents a share, on revenue of $8.3 million. Analysts surveyed by Thomson First Call expected a loss of 22 cents a share. A year earlier, the company posted a loss of $5.4 million, or 25 cents a share, with no revenue. Revenue in the most recent quarter was recorded as part of the company's collaboration and license agreement with Schering AG ( SHR). Sonus shares were trading up 55 cents to $6.35.

Shares of ViroPharma ( VPHM) tumbled 20% after the drug developer said the Office of Generic Drugs may have changed its approach about conditions that must be met by competitors trying to introduce a generic version of the company's Vancocin antibiotic. "Specifically, we were informed that a generic applicant may be able to request such a waiver provided that dissolution testing demonstrates that the test product is rapidly dissolving at certain specified conditions," ViroPharma said. "This deviates from our understanding of OGD's practices which would require, for a nonabsorbed GI drug, a demonstration of bioequivalence through clinical studies or a demonstration of bioequivalence using an appropriately validated in vitro methodology."

ViroPharma said it has attempted to contact the OGD, but it has been unable to confirm the possible change with the agency. Shares were down $3.25 to $12.99.

Merge Healthcare ( MRGE) slumped 11% after the company delayed the filing of its 10-K with the Securities and Exchange Commission. Merge said the delay relates to revenue recognition and tax accounting issues pertaining to its acquisition of Cedara Software in June 2005. Another reason for the delay, Merge said, relates to an investigation of anonymous complaints received by the company. The filing, which was due March 16, won't be filed by March 31, so the company didn't file a 15-day extension with the SEC, Merge said.

As for the company's fourth-quarter results, Merge said it continues to estimate revenue of $23 million to $26 million, which is below analysts' projection of $29.9 million. Merge shares were down $1.94 to $16.03.

Shares of Northfield Laboratories ( NFLD) traded actively after the company said it received an informal request from the SEC for certain information. The probe relates to the clinical development of PolyHeme, a blood substitute product that is used in elective surgery. The company has contacted the SEC, it said, and plans to respond to the request. Shares recently traded up 9 cents to $9.74 on volume of more than 628,000 shares, compared with average daily volume of about 387,000 shares.

Endologix ( ELGX) fell 7% after its independent auditor issued a going-concern qualification in the company's 10-K filing. Based on a history of losses, PricewaterhouseCoopers said there is substantial doubt as to the company's ability to continue as a going concern.

"Based on our expected revenue from sales of the Powerlink System and our ability to adjust certain operating expenses if revenues do not meet our expectations, we believe that our current cash balance, in combination with cash receipts generated from product sales, will be sufficient to fund ongoing operations through at least Dec. 31, 2006," the company said in a press release addressing the going-concern language. "However, if appropriate, we may consider alternatives for additional financing, which could involve equity or debt." Shares were trading down 36 cents to $4.50.

Other health care volume movers included Pfizer ( PFE), up 29 cents to $26.34; Generex Biotech ( GNBT), up 24 cents to $2.86; Novavax ( NVAX), up 3 cents to $7.33; Johnson & Johnson ( JNJ), up 24 cents to $60.26; Elan ( ELN), up 11 cents to $15; Boston Scientific ( BSX), up 19 cents to $22.69; Amgen ( AMGN), down 85 cents to $72.99; Schering-Plough ( SGP), down 12 cents to $18.46; Merck ( MRK), up 31 cents to $35.59; and Bristol-Myers Squibb ( BMY), up 17 cents to $22.99.