A Delaware judge has ruled that two of Pfizer Inc.'s insurers must cover the costs associated with a $486 million settlement in a New York shareholder suit that accused the pharmaceutical giant of misleading investors about the health risks associated with two anti-inflammatory drugs.

The ruling said Pfizer's excess insurers, Arch Insurance Co. and U.S. Specialty Insurance Co., could not rely on a “special litigation exclusion” in their director and officer policies to deny coverage based on another securities class action they claimed was identical to the case in Manhattan federal court.

In a 27-page ruling, Delaware Superior Court Judge Paul R. Wallace sided with Pfizer in finding that though aspects of the cases overlapped, there were still distinct differences between the two, which prevented the insurers from avoiding their coverage obligations.