The account was put up for review following Bayer's purchase of the over-the-counter division of Roche. PHD was the incumbent on the former and MediaCom on the latter.
The $2.9bn purchase of Roche's OTC division has made Bayer one of the biggest consumer health organisations in the world. Its brands include Alka-Seltzer, Rennie and Berocca.
Bayer and Roche's creative accounts, held by Abbott Mead Vickers BBDO and JWT, were unaffected.
Separately, PHD has also won the £33m media planning account for the AA after a head-to-head battle against MindShare. The review was overseen by Kerry Cooper, the director of AA road sales and marketing, with assistance from the media auditor Billetts. The incumbent, Manning Gottlieb OMD, pulled out of the review, leaving MindShare and PHD to fight it out.
The AA called an ad review at the end of last year as part of a wider business review by its new owners, the venture capitalists CVC and Permira.
PHD will work alongside Delaney Lund Knox Warren & Partners, which was appointed last week to AA's loans, insurance and roadside businesses.
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