Pfizer say it is closing its Adelaide manufacturing plant, despite announcing plans to expand the site last year.

The Thebarton factory employs 89 workers to make a chemotherapy drug called pegfilgrastim, which is used around the world.

In March last year, the company was lauded when it announced plans to expand the site at a cost of $21 million.

The South Australian Government at the time said it was a “wonderful sign” of long-term commitment to drug manufacturing.

Pfizer said the upgraded plant would bring a $380 million boost to the South Australian economy over seven years.

The company now says it will consolidate its drug-making operations at other locations.

“This has been a difficult decision, and was based on a number of factors including the existing capacity within Pfizer's global manufacturing network and the efficiency of consolidating manufacturing to fewer locations,” Pfizer said in a statement.

The company says it will redeploy the Adelaide employees elsewhere.