Pharmaceutical conglomerate GSK has split their billion-dollar media planning and buying accounts between fierce rivals WPP and Omnicom, ousting agencies from Publicis and Aegis.

Omnicom's PHD will manage the $450m North America operation, whilst GroupM consolidate the remainder of the global business, with MediaCom holding the £60m UK account.

Publicis' StarcomMediaVest had held the business since GSK's last media review in 2010, alongside Carat and GroupM. Dentsu will continue managing output in Japan.

According to Kantar figures, GSK spent $1.3 billion in 2012, $1.46 billion in 2011 and $1.5 billion in 2010.

"The decision to consolidate our media investment with two network partners – GroupM and OMG, with Dentsu buying in Japan, is based on various factors including simplicity and speedier deployment of best practices," said Sam Singh, vice president of global media at GSK.

"We believe this sets us up with a fit for purpose media system into the future. We continue to hold the outgoing agencies, Starcom and Carat, in the highest of regard. They have consistently exhibited high levels of professionalism and we wish them all the very best."