Pfizer, the world's biggest drugmaker, is selling its swine vaccine business in China to Harbin Pharmaceutical Group for $50 million, a source with direct knowledge of the deal said on Monday.

The disposal was required by the Anti-Trust Bureau of China's Ministry of Commerce as a condition for approval of Pfizer's $68 billion merger with Wyeth, which closed last October, said the source, speaking on condition of anonymity because the deal had not been announced yet.

The deal marked the first time China had ordered a foreign company to divest a locally-based business as a condition for approval of a merger with another foreign company, as part of a review under the country's anti-monopoly law that took effect in August 2008, the source said. Other bidders for the asset included Novartis, Eli Lilly, Boehringer Ingelheim, and Agenix, the source said.

Harbin Pharmaceutical, which counts Warburg Pincus among its major shareholders, manufactures and distributes generic antibiotics drugs in China.