Drugmaker Wyeth on Wednesday sued regulators at the U.S. Food and Drug Administration in an attempt to block the sale of a recently approved generic version of its intravenous antibiotic Zosyn. In the complaint filed in federal district court in Washington, D.C., by Wyeth’s lawyers at Sidley Austin, the company alleges that the generic is not an equivalent product and could harm critically ill patients. The complaint also names as defendants the U.S. Department of Health and Human Services, Secretary of HHS Kathleen Sebelius, and FDA Commissioner Margaret Hamburg.

Zosyn is an intravenous treatment for bacterial infections. Wyeth claims the drug version that the FDA approved last week for manufacture by India’s Orchid Chemicals & Pharmaceuticals Ltd. is based on an old formulation of Zosyn. The old version reacts with a standard IV solution when they are both administered through the same IV line, according to the complaint. The reaction, the complaint says, inactivates the antibiotic, limiting the dosage that patients would get.