Michigan Attorney General Mike Cox has charged a subsidiary of Omnicare Inc. with defrauding the state’s Medicaid system of nearly $5 million since 1998.

State officials have said their investigation is ongoing and more charges could come against Specialized Pharmacy Services. Omnicare is the nation’s biggest provider of pharmaceuticals to nursing homes, assisted living and other long-term care settings.

Other states as well as the federal government also are investigating allegations that subsidiaries of Omnicare fraudulently switched nursing home patients to more-expensive prescription capsules of the same medication. In recent years, the company has reached settlements with Maine and New York over Medicaid fraud allegations and billing irregularities.