Pfizer Inc. will pay $2.3 billion to settle a U.S. investigation into illegal marketing of medicines, the largest agreement in such a case, and a subsidiary will plead guilty to a criminal charge.

The amount, which Pfizer disclosed in January, includes $1.3 billion to close the criminal part of the investigation, the New York-based company said today in a statement. Pharmacia & Upjohn Co., acquired by Pfizer in 2003, will plead guilty to a count of felony misbranding of a pharmaceutical, according to a Justice Department summary of the agreement.

The criminal case stems from promotion of Bextra, a painkiller that Pfizer, the world’s largest drugmaker, acquired through Upjohn and withdrew in 2005 because of its connection with a rare skin condition. Investigators also looked at practices, including kickbacks to doctors in the sale of nine other drugs, among them the impotence drug Viagra and cholesterol treatment Lipitor, the company and government officials said.