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Genzyme Corp. has filed a patent infringement suit against Impax Laboratories Inc. focused on the kidney dialysis drug Renvela.

The Hayward-based generic drug maker (NASDAQ: IPXL) said Genzyme filed the suit Thursday in U.S. District Court in Maryland for the 2.4-gram and 0.8-gram versions of sevelamer carbonate tablets, which are used to control serum phosphorus in chronic kidney disease patients on dialysis.

According to drug-sales tracker IMS Health, Renvela had U.S. sales of $200 million in the 12 months ended March 31.

Genzyme’s (NASDAQ; GENZ) patent on Renvela and another dialysis product, Renagel, expire in 2013.

Genzyme’s suit formally initiates the patent challenge process under the Hatch-Waxman Act, Impax said. Without such a challenge, the Food and Drug Administration could not approve Impax’s abbreviated new drug application, or ANDA.

If a patent is successfully challenged, the first generic drug maker to allege that the patent is invalid or not infringed is entitled to a 180-day period of market exclusivity over manufacturers of other generics cash advance now.

Lupin Pharmaceuticals Inc. and Watson Pharmaceuticals Inc. are among the generic drug makers hoping to sell lower-cost versions of Renvela.

Impax last year had filed its application with the Food and Drug Administration for generic 400-milligram and 800-milligram sevelamer hydrochloride tablets and 800-milligram sevelamer carbonate tablets.

Genzyme, based in Cambridge, Mass., initially filed a patent infringement suit regarding Renagel in March 2009 and regarding Renvela in April 2009. Impax responded that two key Genzyme patents are invalid or not being infringed by Impax’s proposed generics.

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