It has been reported that the US drug research firm, Charles River Laboratories, has approved to purchase Wuxi PharmaTech, a Chinese rival, for US$1.6bn, since western pharmaceutical firms raise outsourcing of their study and progress services to the east.

With the deal Charles River would be allowed to increase its presence in China and achieve greater access to the nation's large supply of scientists and cheap R&D services.

The Massachusetts-based company is one of the largest drug contract researchers globally, which provide R&D services to drug makers.

"It's an ongoing trend as a result of the change in dynamic in the R&D world. China is attractive because of the availability of scientists and better value for money," said Du Jinsong, analyst at Credit Suisse.

According to Credit Suisse, R&D work in the findings of drugs was entirely domestic in 1997. In 2009, about one-fifth of that was outsourced.

Under the transaction, declared on Monday, Charles River, recommended by JPMorgan, will pay Wuxi, advised by Credit Suisse, $21.25 a share in money and stock.

The firm will maintain the name Charles River and Wuxi will be removed from the list.

According to Dealogic, the deal is amid the top three overseas captures of a Chinese firm and the chief in the pharmaceutical company.