Quintiles’ (NYSE:Q) public stock offering last week was the Triangle’s biggest IPO ever and it’s gotten even bigger.

The Durham company’s $947 million IPO included the option for underwriters of the offering to purchase an additional 3.5 million shares. That overallotment closed today. With Quintiles selling a total of 27.2 million shares at $40 per share, the company’s tally from the IPO now tops $1 billion.

Morgan Stanley, Barclays and J.P. Morgan served as joint book-running managers and as representatives of the underwriters for the offering. Of the total shares sold in the public offering, 13.1 million shares came from the company. Quintiles will see $496.1 million in proceeds, according to the prospectus, which Quintiles will use to pay down debt and reinvest in the company.

Company insiders, including the investors who had taken stakes in Quintiles when the company was private, sold 10.5 million shares in the IPO. The additional shares in the overallotment were offered to underwriters by these selling shareholders, who will see proceeds of more than $533.4 million.

Quintiles is the largest provider of biopharmaceutical services to biotechnology and pharmaceutical companies. Quintiles closed today at $44.43 per share, up 2.56 percent from Monday’s close and up 11 percent from the IPO price.

[QUINTILES ARCHIVE: Check out more than a decade of Quintiles stories as reported in WRAL Tech Wire.]