Merck will consolidate media duties on all of its brands, including the newly acquired Schering-Plough portfolio, after a review.

The move, first reported by Adweek, puts the combined account – valued at approximately $600 million without digital spend, according to Nielsen figures – up for grabs, with Merck’s incumbents Draftfcb and Initiative participating.

Schering-Plough incumbent Havas MPG is also in on the pitch, with final presentations planned for this March. Publicis Groupe’s Zenith Media will also participate in the review, sources told Adweek. Participating agency sources verified the account review with MM&M, but couldn’t offer any additional information or details, citing sensitivity on the issue. A spokesperson at Merck refused to confirm the review.

Merck alone is responsible for the bulk of the $600 million account, spending upwards of $520 million from January-November 2009. Draftfcb has previously handled planning and some buying, including digital and print. Initiative handles TV buying, according to the Adweek report.

Creative agencies that work on Merck and Schering brands, including Draftfcb, DDB Healthcare, Havas’ Euro RSCG, Merkley + Partners, BBDO and TBWAWorldHealth, are not included in the media-only review, per Adweek sources.

Interpublic Group’s Initiative agency has fared well in large pharma media consolidations of late. Bayer consolidated its US media account with Initiative last November.