Sykes is joining the firm as board director of communications for its DePuy Orthopaedics operations in the UK, EMEA and Asia Pacific.
DePuy is a developer, manufacturer and distributor of hip and knee replacements, and spinal implants.
Sykes will start the new role at the end of March, covering external, internal and patient communications. She will be based in Leeds and report to international president Richard Twomey.
She will be succeeded at AstraZeneca by Amie Malkin, who joined last year as head of comms from Burson-Marsteller's London healthcare practice, where she was MD and chairman.
Sykes has been at AstraZeneca for six years and has led a PR and comms team of 30 people across nine UK sites, covering corporate, internal and external affairs.
Most recently, Sykes has been carrying out a global review of comms resources for AstraZeneca's IT teams.
Her departure coincides with the hire of Sameena Mirza as senior comms manager. Mirza joined last week from Huntsworth Health, where she was client services director in medical comms.