Hughesman, who holds the title comms team leader, has been replaced on an interim basis by brand comms manager David Prager.
Hughesman is understood to be poised to join WPP-owned agency Hill & Knowlton. She was unavailable to comment as PRWeek went to press.
H&K, which has AZ as one of its top UK healthcare clients, declined to comment.
Hughesman's former AZ role, based in the firm's Luton offices, oversees a three-strong team handling UK corporate messaging for drugs brands.
The company has had to deal with a raft of product-related PR challenges over drugs such as cholesterol-buster Crestor and lung cancer product Iressa.
AZ withdrew its application to market Iressa across Europe in January after a disappointing trial, while Crestor has faced concerns about its safety.
Prager continues to hold his role as brand comms manager (Symbicort) while handling Hughesman's former role on an interim basis. Hughesman's permanent replacement has yet to be chosen.
Hughesman has formerly worked at WPP-owned agency Ogilvy PR Worldwide in London as an associate director.
AZ beat City forecasts last week when it posted first-quarter pre-tax profits of around £775m - up a third on last year - with global sales up nine per cent on the first quarter of 2004.