The media agency won both of the pieces of business for the two companies, which used to be part of the Kingfisher Group, from the incumbent agency, Bates, following a pitch.
Bates traditionally handled all strategic planning for the Kingfisher Group companies but this has diminished over time.
Superdrug, the pharmacy chain, and the music and entertainment store MVC demerged from the Kingfisher group in 2001. Superdrug was bought by the Dutch drugs company Kruidvat Beheer while MVC was aligned to Woolworths.
Zenith originally won the centralised £70 million Kingfisher account in 1995 and has worked on all of its companies ever since.
It has gradually strengthened its relationships and now the only former Kingfisher company that does not use Zenith for its strategic media planning is B&Q, which continues to use Bates. However, Zenith does handle media buying for the DIY superstore chain.
Tom George, the managing partner at Zenith, said: "We have always enjoyed an excellent relationship with Superdrug and we were able to demonstrate that our media planning credentials could help add more value to the media process."
Liza Fenwick, the advertising manager at Superdrug, added: "It's great to extend our relationship with Zenith. It has been providing us with excellent media buying solutions for the past ten years and has helped us to deliver our customer communications efficiently and effectively."