Double-digit revenue growth at contract research organization Quintiles Transnational Holdings Inc. is paying off in spades for the company's financial sponsors -- Bain Capital LLC and TPG Capital -- which are poised to reap yet another special dividend through a debt issuance.

Durham, N.C.-based Quintiles is paying a $335 million payout to investors, which include 3i Group plc and Singapore's state-owned Temasek Holdings Pte. Ltd. Quintiles is making the payment through a $300 million senior secured term loan and $50 million in cash, a source said Thursday, Feb. 23.

The $335 million dividend comes on top of $917 million Quintiles has paid shareholders since the beginning of 2009. The $1.25 billion total to date includes a $300 million dividend it paid in May 2011 when the services provider refinanced its existing debt, or about $2.225 billion, according to Moody's Investors Service.

Bain and TPG didn't disclose financial terms when they bought Quintiles in late 2007 from One Equity Partners, an investment arm of J.P. Morgan Chase & Co. Reports at the time said the deal was worth around $3 billion.

Quintiles is among the top performers in the booming contract research organization industry. Its revenue stood at $3.2 billion for the year ended Sept. 30, up from $3 billion in 2010, according to Moody's.

Contract research organizations such as Quintiles provide clinical testing and commercialization services, among others, to pharmaceutical and biotech companies. They have experienced substantial growth in recent years as pharmaceutical companies look to cut costs of research and development.

"As a result, we're taking that strong performance and making a return on investment to shareholders," said Phil Bridges, a Quintiles spokesman.

Bridges said the company's growth has also allowed it to make internal investments and acquisitions. Quintiles made three acquisitions in one week during 2011, and and plans to be a buyer in 2012, he said.

The 7.5% fixed $300 million term loan Quintiles is using to finance the dividend broke for trading Wednesday at 97.959 to yield 8%, a source said. The loan is callable for three years at 102, then at 101 and at par in the fifth year. J.P. Morgan, Morgan Stanley and Barclays Capital arranged the loan, first reported by Standard & Poor's Leveraged Commentary & Data.

The new term loan is rated B1 by Moody's, as are Quintiles' other loans and its corporate family rating. S&P gave the new term loan a B rating and confirmed a BB- corporate family rating.

Jessica Gladstone, a senior analyst in the corporate finance group at Moody's, said Quintiles' fundamentals are probably stronger than the B1 rating Moody's assigned. However, she said, the rating reflects the company's propensity to leverage up to pay shareholder dividends.

"They'll reduce leverage through Ebitda growth; because they're so aggressive at returning capital to shareholders, we've always kept them at a B1," she added.

S&P said it expects Quintiles to continue making dividend payments, keeping a debt-to-Ebitda ratio in the 4 times range.

Quintiles has a $225 million senior secured revolving credit facility maturing in 2016 and a $2 billion senior secured term loan B due in 2018.

Bain, TPG and 3i declined to comment.