Shares of

Threshold Pharmaceuticals

(THLD)

were among the worst-performing health-related stocks Friday, plummeting 76% after the

TST Recommends

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) 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) 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.

Illumina

( PCOP) fell 6% after the genetics diagnostics company said it plans to sell 3.5 million shares of stock in a public offering. The company also granted underwriters an option to buy an additional 525,000 shares to cover over-allotments. Goldman Sachs and Merrill Lynch are leading the underwriting syndicate. The company plans to use proceeds from the offering to fund research and development, manufacturing capacity, and working capital needs. Shares were trading down $1.61 to $26.80.

Shares of

Pharmacopeia

( SGP) slid 13% after the company posted a wider-than-anticipated first-quarter loss. The company posted a loss of $7.7 million, or 51 cents a share, on revenue of $4.12 million. Analysts expected a loss of 32 cents a share and revenue of $4.86 million. During the year-earlier quarter, the company posted a loss of $4.6 million, or 38 cents a share, on revenue of $5.7 million. Pharmacopeia blamed the revenue decline on a reduction in funding from its collaborations with

Schering-Plough

( SGP) and the expiration of other collaborative agreements. Shares were trading down 79 cents to $5.11.

Other health care volume movers included

Pfizer

(PFE) - Get Report

, down 25 cents to $24.56;

UnitedHealth Group

(UNH) - Get Report

, up $1.44 to $45.81;

Boston Scientific

(BSX) - Get Report

, down 46 cents to $20.81;

Johnson & Johnson

(JNJ) - Get Report

, up 12 cents to $58.96;

Elan

(ELN)

, up 88 cents to $15.68;

Teva Pharmaceutical

(TEVA) - Get Report

, up 10 cents to $37.44;

Amgen

(AMGN) - Get Report

, up 85 cents to $68.13;

Medtronic

(MDT) - Get Report

, down 11 cents to $48.64;

Aetna

(AET)

, up 4 cents to $39.75; and

Schering-Plough

( SGP), up 2 cents to $19.11.