Global pharmaceutical giant Abbott Laboratories has agreed to pay federal and state governments $1.6 billion in criminal and civil fines for illegally promoting unapproved uses of its drug Depakote, including to sedate elderly patients in nursing homes, officials announced Monday.

The settlement, which includes an agreement to plead guilty to a criminal misdemeanor, is the second largest in a string of multimillion-dollar payouts in recent years resulting from stepped-up enforcement by the Justice Department and state investigators against drugmakers that “misbrand” their products.

While doctors can — and frequently do — prescribe drugs for purposes beyond those approved as “safe and effective” by the Food and Drug Administration, it is illegal for manufacturers to actively market their products for such off-label use.

“Not only did Abbott engage in off-label promotion, but it targeted elderly dementia patients and downplayed the risks apparent from its own clinical studies,” Tony West, acting associate attorney general, said in a statement.

In 2009, Pfizer paid the largest settlement to date in such a case — $2.3 billion in connection with its marketing of drugs that included the painkiller Bextra. Last year, British drugmaker GlaxoSmithKline announced that it expects to reach a bigger settlement this year related to its development and promotion of the diabetes drug Avandia, among others.

Abbott’s settlement marks the culmination of a four-year investigation into an array of strategies the Illinois-based multinational employed to vastly expand the market for its neurologic drug Depakote, which the FDA has approved to treat three conditions: epileptic seizures, migraines, and the manic episodes experienced by people with bipolar disorder.