NEW YORK (AP) — Warner Chilcott Ltd. said Thursday it is suing Impax Laboratories Inc., accusing Impax of infringing a patent supporting 150 milligram tablets of Warner Chilcott’s acne medication Doryx. Bermuda-based Warner Chilcott said it believes the lawsuit will prevent the Food and Drug Administration from approving Impax’s generic version for up to 30 months, or until a district court makes a ruling on the patent. It sells the drugs through a partnership with Hospira Inc.’s Mayne Pharma International unit. Impax says sales of 150 mg Doryx tablets reached $29 million in the 12 months ended January 2009. The company did not immediately return calls seeking comment. Warner Chilcott is also suing Impax for patent infringement on 75 mg and 100 mg doses of Doryx, but it was not able to delay FDA rulings on those versions of the drug.