By Lauren Pollock 
 

Baxter International Inc. (BAX) said it received another request for additional information from the U.S. Food and Drug Administration related to its investigational product HyQ, which is in development with Halozyme Therapeutics Inc. (HALO), following a similar letter in April.

The FDA's request delays any potential approval of HyQ, a treatment that aims to allow physicians to tailor antibody drug therapy to the lifestyle and medical needs of patients with immune-system disorders.

Halozyme shares plunged 50% to $4.25 after hours, while Baxter was unchanged at $58.63.

The FDA's latest letter seeks additional preclinical data to support the application. The primary issues raised in the letter focus on non-neutralizing antibodies generated against recombinant human hyaluronidase and the possible effects of these antibodies on reproduction, development and fertility.

HyQ, which is based on a Baxter IV drug, targets a condition called primary immunodeficiency, which can involve any of more than 150 diseases that cause the immune system to function poorly or not at all. At least 250,000 Americans have the condition, many of them children.

HyQ is infused under the skin but, like intravenous treatments, appears to only need infusions every three or four weeks.

Baxter said it plans to file an amendment to the application for HyQ following additional talks with the FDA. Patients enrolled in ongoing HyQ studies will now be treated with Baxter's immune globulin therapy without recombinant human hyaluronidase, at the FDA's request.

The prior request had to do with chronic long-term data on an ingredient in the drug.

Write to Lauren Pollock at lauren.pollock@dowjones.com

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