Halozyme Plummets After U.S. Regulators Reject Drug

Halozyme Therapeutics Inc. (HALO) fell the most in its eight-year history after an immune deficiency treatment it developed with Baxter International Inc. (BAX) was rejected by U.S. regulators who also halted a separate clinical trial involving Halozyme’s part of the combination therapy.

Halozyme dropped 50 percent to close at $4.30 in New York, the biggest single-day decrease since its began trading publicly on March 15, 2004.

The drug, called HyQ, combines immune globulin made by Baxter with Halozyme’s product, a recombinant human hyaluronidase. The Food and Drug Administration requested additional pre-clinical data for the product in its rejection letter, the companies said yesterday in a statement.

Halozyme “can directly address the questions raised by,” the FDA, Gregory Frost, president and chief executive officer, of the company, said in the statement. The primary concern is the product’s potential effect on reproduction, development and fertility, according to the statement.

Baxter, based in Deerfield, Illinois, fell 1.2 percent to $57.95.

The trial stopped by the agency combined the product made by San Diego-based Halozyme with ViroPharma Inc. (VPHM)’s Cinryze because of safety concerns, Exton, Pennsylvania-based ViroPharma said in a statement. Halozyme also must provide the FDA results from added pre-clinical tests before the trials can resume.

ViroPharma is preparing to begin a trial that will evaluate the safety and efficacy of two different doses of Cinryze as a standalone therapy, the company said. Cinryze treats hereditary angioedema, which is a disease that causes severe swelling in the limbs, face, intestinal tract and airway.

To contact the reporters on this story: Anna Edney in Washington at aedney@bloomberg.net; Jeanna Smialek in New York at jsmialek@bloomberg.net

To contact the editor responsible for this story: Reg Gale at rgale5@bloomberg.net