Several sources with knowledge of the process said GSK had started the talks ahead of a formal review process and was hoping to appoint a single media agency network. It is unclear whether the review will be confined to or extended beyond roster networks.
WPP’s MediaCom handles GSK’s £60 million UK media account, while Omnicom’s PHD picked up the $1.4 billion (£890 million) US business in late 2010.
MediaCom lost the US account and some European markets, to Starcom Media-Vest Group, as part of two separate reviews in 2010.
WPP will hope to strengthen its relationship with GSK as its part-owned agency CHI & Partners has just won the Maxinutrition ad business. Grey picked up a global brief to create a corporate "masterbrand" campaign in December last year.
The global media review comes as GSK confirmed plans to restructure its European pharmaceuticals operation to cut costs and announced a "strategic review" of Lucozade and Ribena, after it reported a 1 per cent revenue decline in 2012.
GSK hired Sameer Singh, the former Procter & Gamble vice-president of media in Asia and China, to the new position of vice-president and head of global media in September 2012.
Singh was given a brief to spearhead a new approach to media planning, buying and strategy but, at the time, a spokesman said it would have no "immediate" implications for its media agency roster.
A GSK spokeswoman told Campaign this week: "GSK is creating the world’s best fast-moving consumer healthcare company. Our approach to media planning, buying and strategy will support this."