Today's Health Winners and Losers

Shares of Threshold Pharmaceuticals(THLD Quote) were among the worst-performing health-related stocks Friday, plummeting 76% after the Food and Drug Administration put the biotechnology company's clinical development program for a benign prostatic hyperplasia treatment on partial clinical hold.

The FDA suspended the prostate drug trial because of abnormalities observed in liver enzyme levels in six patients. "These abnormalities include 3 serious adverse events observed at 3 months of dosing in the Phase III European/Canadian clinical trial and 3 additional observations of elevated liver enzymes that occurred in other ongoing clinical trials," the company said.

Threshold said it plans to amend its Phase III European/Canadian trial and discontinue dosing for the 567 patients enrolled in the study. "Our main priority right now is the safety of our patients and we are working with the FDA to resolve these safety issues as quickly as possible," Threshold said. Under the partial hold, the company still will be allowed to complete a Phase II trial. Shares were trading down $10.68 to $3.32.

Barr Pharmaceuticals(BRL Quote) fell 5% after the Patent and Trademark Office rejected the company's application for reissue of a patent related to the Seasonale oral contraceptive. Because the company received a "non-final rejection" notice, Barr's Duramed unit will have three months to respond to issues raised by the PTO. "While we are disappointed in the determination by the PTO, we intend to fully review all options available to protect our patentable invention, and will respond to the non-final rejection as quickly as possible," Barr said in a press release. The patent is scheduled to expire in September. Barr shares were trading down $2.89 to $50.75.

Shares of American Oriental Bioengineering(AOB Quote) jumped 10% after the developer of plant-based pharmaceutical products posted big jumps in first-quarter earnings and revenue. The Chinese company earned $4.9 million, or 8 cents a share, on revenue of $19.1 million. A year earlier, the company earned $2.2 million, or 5 cents a share, on revenue of $9.7 million. "The company experienced strength across all product lines which reflects the success of our efforts to continue to increase brand awareness and further penetrate underserved and rapidly growing markets throughout China," American Oriental said. Shares were trading up 50 cents to $5.64.