Pfizer has agreed to pay $491m (£320m) to settle an investigation into illegal marketing of the drug Rapamune by Wyeth, a company it acquired in 2009.

Sales staff at Wyeth allegedly encouraged doctors to prescribe Rapamune, a drug prescribed to prevent the rejection of transplanted kidneys, for other non-approved organ transplants.

US based Pfizer has stressed that the alleged illegal marketing took place before Wyeth was purchased by the company.

The US Department of Justice is quoted by the BB as saying: "Wyeth trained its sales force to promote Rapamune for off-label uses not approved by the FDA, including ex-renal uses, and even paid bonuses to incentivize those sales."

Pfizer said in a statement: "Pfizer was not a subject or target of this matter, and cooperated fully with the government from the time it learned of this investigation in October 2009."

Last year, Pfizer agreed to pay $55m to settle other charges that Wyeth promoted heartburn drug Protonix for unapproved uses.

This latest payout comes after Pfizer recorded excellent profit figures. According to the company, its profit quadrupled during the second quarter with a net profit of $14.1bn during the period, compared to $3.2bn during the same period a year ago.

Image: Pfizer’s headquarters. Photo: courtesy of Jim.henderson.