New York-based Pfizer Inc. has agreed to plead guilty to criminal charges of illegally promoting the sale of its painkiller, Bextra and other drugs for non-FDA approved uses.

Terms of the agreement call for the drug giant to fork over $2.3 billion in fines. That’s the largest penalty ever assessed for such marketing shenanigans.

Pfizer announced last winter that it had taken a $2.3 billion settlement-related charge for Q4, 2009, but details of the agreement hadn’t been made public until now.

The details are that Pfizer encouraged physicians to prescribe Bextra for off-label uses like acute pain, its atypical antipsychotic Geodon for off-label use by children, and similar behavior involving Zyvox, an antibiotic, and Lyrica, an epilepsy drug.

US physicians are permitted to prescribe FDA-approved drugs for anything they want,  but drug companies are not allowed to market drugs for unapproved uses.

The settlement involved Pfizer’s Pharmacia & Upjohn unit and the Departments of Justice and Health and Human Services.

Pfizer yanked Bextra in 2005, shortly after Merck had pulled the plug on its painkiller, Vioxx, after the latterwas shown to increase the risk of heart attacks.

Terms of the settlement also resolve allegations that Pfizer comped doctors for meals, subsidized their travel and paid honoraria for speaking engagements to induce them to prescribe these drugs for off-label uses.

Remarkably, the settlement represents the third time in which Pfizer has been required to sign a “corporate integrity” agreement pledging to clean up its act. It signed similar agreements in 2002 regarding Lipitor and in 2004 for Neurontin.