Reuters reported the development, citing people familiar with the matter.
Bain and TPG bought into the company in 2008 by taking a stake from One Equity Partners in a deal which valued the company at about $3.8bn.
They joined an investor group consisting of Singapore sovereign wealth fund Temasek and Quintiles founder and CEO Dennis Gillings.
The UK’s 3i Group is also a minority investor, holding a seven per cent stake.
Quintiles, which is the world’s largest provider of testing services to drugmakers, had revenues of about $3.5bn in the 12 months ending June 2012.
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