Sanofi-Aventis of France has filed a lawsuit against the U.S. Food and Drug Administration to suspend its approval of a genetic version of the company’s Lovenox blood thinner.

In the complaint, Sanofi said the generic isn’t “clinically equivalent” to the low-molecular-weight heparin product Lovenox, and the FDA’s decision may cause Sanofi “irreparable harm.”

Sanofi-Aventis’s second best selling drug Lovenox is an anti-coagulant drug that comes in an injectable format and works to prevent blood clots and vein thrombosis by thinning the blood inside the body.

A lower-cost copy of Lovenox was developed through a collaboration between Sandoz, the generic division of Novartis, the Basel, Switzerland-based drugmaker, and Momenta, a biotechnology company in Cambridge, Massachusetts.

A spokeswoman for Sandoz said genetic enoxaparin sodium injection began shipping immediately following FDA approval on July 23.

Sanofi believes that the FDA’s approval “was not made in accordance with the agency’s statutory obligations,” according to a statement emailed by the company’s spokesman Jean-Marc Podvin. He added that the approval “poses a number of significant questions regarding the FDA review process for complex pharmaceutical products which are important to pursue.”

Sanofi contends that their brand drug’s ingredient made from sugar molecules found in heparin, a substance derived from pig intestines, is too complex to be copied with precision by makers of generic versions.

Patent on Lovenox was voided last year because Sanofi had misled the US Patent and Trademark Office, according to a ruling by the US Supreme Court. The company’s appeal for reinstatement of the patent was rejected by the Court.

The company’s request for a temporary restraining order to stop sales of the generic drug this week was denied by the U.S. District Court for the District of Columbia.

The case, Sanofi-Aventis US LLC v. Food and Drug Administration 10cv1255, will be heard by the federal court on August 17.