AstraZeneca will expand its manufacturing facility in Frederick, Md., and hire an additional 300 workers at the site. (Phil Noble/Reuters)

British drugmaker AstraZeneca plans to spend $200 million over the next three years, expanding its manufacturing facility in Frederick, Md., and hiring an additional 300 workers at the site, executives said.

The decision further cements Gaithersburg-based MedImmune, an AstraZeneca company, as the crown jewel of Maryland’s life sciences industry. AstraZeneca and MedImmune are the state’s largest biotechnology employers, with a total of 3,100 staffers, and executives there have started numerous smaller firms.

The biologics manufacturing facility in Frederick is already AstraZeneca’s largest such site in the world, with a half-million square feet of administrative, warehouse, laboratory and production space.

The expansion will begin next month and add 40,000 square feet. The additional space is expected to accommodate the company’s growing manufacturing needs as its six drugs currently in third-phase trials to treat cancer, autoimmune diseases and respiratory illness move toward the market.

“The products we’re working on are coming to late stage so the need for more manufacturing to prepare, if we’re successful, for commercial-grade products is very important,” said Bahija Jallal, executive vice president and head of MedImmune.

The company will also hire 300 employees in administrative, laboratory and manufacturing roles. A spokeswoman said the company expects to fill most of those positions by 2017.

The latest job gains add to the 300 positions that were transferred to Maryland early last year when AstraZeneca announced it would consolidate its operations and designated the state as one of three global research and development centers for the company. The others are located in the United Kingdom and Sweden.

AstraZeneca first planted its flag in Maryland in June 2007 when the drugmaker paid a staggering $15.6 billion to acquire MedImmune, a life sciences company that specialized in developing biologics.

Since then, the parent company has progressively shifted more research and development resources to its Maryland outpost. The treatments being developed at MedImmune now represent nearly half of AstraZeneca’s pipeline.

“It is an example of a how an acquisition of an existing asset in the state can be quite a positive thing,” said Judy Britz, executive director of the BioMaryland Center, which is part of the state’s economic development department.

While AstraZeneca’s investment will bring tangible economic benefits to Maryland, it’s also symbolic of the state’s life sciences potential, said Doug Doerfler, chief executive at MaxCyte and chairman of the Tech Council of Maryland, a trade association.

“Given the fact that they’re investing in all parts of the value chain, the discovery, development, manufacturing and commercialization, it really speaks to the ability of Maryland to be able to develop and support those capabilities,” Doerfler said.