The community pharmacy chain is owned by German pharmaceuticals company Celesio.
It has more than 1,600 pharmacies across the UK, based in community and health centre locations.
It is understood that APCO, headed in the UK by MD Darren Murphy, was invited to re-pitch and has made the final three. The other two agencies are believed to be Lexington Communications and Insight Public Affairs.
A decision is expected later this month.