UPDATE 1-Teva exclusive on hypertension drugs challenged

* Apotex, Roxane Labs challenge Teva exclusivity

* Teva says court decision protects exclusive to the drugs (Recasts with additional company challenging decision; adds response from FDA, Teva)

WASHINGTON, March 31 (Reuters) - Two generic pharmaceutical manufacturers have challenged the U.S. Food and Drug Administration's decision to give rival Teva Pharmaceutical Industries Ltd TEVA.TA six months of exclusive marketing for generic versions of widely-used blood pressure medicines.

Apotex Inc and Roxane Laboratories filed lawsuits this week against the FDA and its parent agency, the Department of Health and Human Services, arguing that a key patent for the drugs, known as Hyzaar and Cozaar, had expired and therefore no company was eligible for the exclusive rights.

Three patents were associated with the medicines: one that expires April 6 and two others that have expired.

Earlier this month a U.S. appeals court found in favor of Teva to market the generic forms of the drugs exclusively for six months after the manufacturer Merck & Co Inc MRK.N had one of the patents delisted and it subsequently expired.

Apotex said notwithstanding the court ruling, that patent had expired and no exclusivity was allowed. The FDA’s “decision erroneously assumes that the FDA may deviate from the clear intent of Congress with regard to patent expiration,” it said.

Apotex and Roxane both filed applications with the FDA to offer generic versions of the drugs and said in the court filing that they were prepared to compete with Teva if they won approval by April 6 from the FDA.

The FDA and HHS argued in a reply brief that the appeals court ruling for Teva would also apply for the expiration of the patent at issue. “The relief Apotex seeks is not warranted,” the agencies said.

Teva in its own filing said the district court cannot ignore the earlier appeals court ruling. “That is madness, and this court should reject plaintiffs’ invitation to Wonderland.”

The two drugs had combined worldwide sales of $3.6 billion in 2009, of which U.S. sales were about $1.5 billion, according to Teva.

While branded drugs can lose as much as 80 percent of revenues once generic versions flood the market, the erosion is typically slower when just one generic competitor steps in.

The exclusivity period is usually awarded to the first company that files with U.S. health regulators seeking approval for a generic drug, and that lets the company charge a bit more for its drug before competition forces cheaper pricing.

Apotex asked the U.S. District Court for the District of Columbia to nullify the FDA’s decision favoring Teva and bar the agency from giving the company a six-month exclusive marketing period for the medicines.

Teva’s shares closed down 49 cents, or less than 1 percent, to $63.08 on Nasdaq.

The case is Apotex v Sebelius, U.S. District Court for the District of Columbia, case no. 10-00517. (Additional reporting by Lisa Richwine, editing by Tim Dobbyn)