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.