Pfizer is to let 180 workers go at its two Cork plants in Little Island and Ringaskiddy, with staff to be briefed on the job losses later this week.
The Irish Examiner understands that between 120 and 130 jobs will go at the Ringaskiddy plant and the remainder at Little Island, where the cholesterol reduction drug Lipitor is produced.
Lipitor came off patent in America in Nov 2011 and in Europe last month, resulting in fears among the Little Island workforce that the plant would be closed and production transferred to the Ringaskiddy facility.
Lipitor is the biggest selling medicine in the world, earning Pfizer $14bn (€11.2bn) a year.
The fallout from expiration of patent, and other medicines due to come off patent, is that the company is seeking to cut €80m from its Irish operations.
Job losses will be across the board. The pharmaceutical company currently employs more than 700 workers at both Cork plants, 500 in Ringaskiddy and 220 in Little Island.
News of the job losses comes following months of speculation about a major costs reduction programme by the pharmaceutical giant.