Yesterday, GlaxoSmithKline (GSK) begun a review of its global media planning and buying business.

Now, AdWeek has revealed the six agencies invited to pitch for the multi-billion dollar account.

All six major media agencies have been invited to pitch; WPP, Omnicom, Publicis, Dentsu, Havas and IPG.

The news of the review follows the three-year contracts with incumbent agencies PHD and MediaCom drawing to a close, having won the account in 2015.

This was two years after GSK consolidated its media account with GroupM in 2013, keeping on PHD as its lead media agency in the US.

According to Ad Age, GSK spent roughly $US1.7 billion on advertising in 2017.