Cambridge biopharmaceutical company Sarepta Therapeutics has started retrofitting a building it purchased from another biotech company more than two years ago.

The project, located at the 100 Federal St. building formerly owned by Eisai, is scheduled to be fully operational sometime in the first quarter of next year.

The 60,000-square-foot facility has been closed since 2013, when Japanese drug developer Eisai downsized and closed that facility’s doors but kept open another Andover property. Sarepta purchased the shuttered property in 2014 for nearly $15 million.

“We wanted to increase our presence in Massachusetts,” said Sarepta spokeswoman Sarah Bard in an email to the Townsman.

And now, more than two years later, Sarepta is putting the building to use. Approximately 45 employees will be employed and stationed at the Andover facility, Bard said, and the company as a whole currently employs approximately 200 full-time employees.

Andover Building Inspector Chris Clemente confirmed that the company was issued a permit on Sept. 23 of this year for an interior fit-up of 45,000 square feet. A rough inspection was done on Oct. 20, he confirmed, and the work is being completed by Timberline Construction at the cost of $445,000.

Sarepta’s main focus, according to its website, “is to transform how the world approaches the treatment of serious and life-threatening diseases by unlocking the potential of RNA-based technologies.” Their Andover location will focus on preclinical research and manufacturing, according to their team.

Sarepta’s newest drug, Exondys 51, which aims to slow the onset of Duchenne muscular dystrophy, or DMD, was approved by the U.S. Food and Drug Administration (FDA) on Sept. 19.

DMD is a rare genetic disorder characterized by progressive muscle deterioration and weakness. It is the most common type of muscular dystrophy, caused by an absence of dystrophin, a protein that helps keep muscle cells intact. The first symptoms are usually seen between three and five years of age, and worsen over time. The disease often occurs in people without a known family history of the condition and primarily affects boys, but in rare cases it can affect girls, and occurs in about one out of every 3,600 male infants worldwide.

According to the FDA, those with DMD progressively lose the ability to perform activities independently and often require use of a wheelchair by their early teens. As the disease progresses, life-threatening heart and respiratory conditions can occur. Patients typically succumb to the disease in their 20s or 30s; however, disease severity and life expectancy vary.