Margot Rozga and Matthew Baker have become the latest recruits to David Rowley's Open Health, which launched in January 2011.
Rowley left Huntsworth in 2009 after eight years to set up the new agency.
Chime Communications, a direct rival to Huntsworth, funded the start-up of Open Health and is financially backing the firm as it seeks to expand in the healthcare space.
An industry source said that Open Health would 'almost certainly be considered a rival to Huntsworth's companies'.
Rozga, who was previously senior account director at ApotheCom, Huntsworth's global medical comms agency, will drive the medical comms business at Open Health.
She joins as associate partner and is reunited with founding partners Sandy Royden, former head of Europe, Huntsworth Health; Marcus Perry, president of Nitrogen North America, also a Huntsworth Health firm; and Roger Selman, former chief finance director at Huntsworth Health Global.
Baker joins the firm as part of Open Health's recent acquisition of healthcare advertising agency Lane Earl Cox. As MD of LEC, he will head the newly created Open LEC.
Baker joined the ad agency from Huntsworth Health, where he was director of digital comms and director of brand strategy, in March 2010.
As part of the venture, life science and healthcare agency De Facto Communications, which is part of Chime, also became part of Open Health.