US pharmaceutical giant Pfizer said on Wednesday fourth-quarter net income nearly tripled from a year ago to $865.5 million, after acquiring rival Wyeth.

"During the fourth quarter, we closed the Wyeth acquisition and immediately began the integration of our operations, advancing the transformation of the company,'' Pfizer chairman and chief executive Jeff Kindler said in a statement on Tuesday.

"We are pleased with the rapid pace of the integration and our ability to quickly realise the benefits of our combined organisation.''