On Monday, GSK announced it will spend $139m (€127m) to increase active pharmaceutical ingredient (API) manufacturing capacity at the facility by around 50%.
The UK-headquartered firm said the expansion was driven by demand for its systemic lupus erythematosus (SLE) drug Benlysta (belimumab).
GSK also plans to make a self-injection formulation of Benlysta at the facility if it the drug wins US Food and Drug Administration (FDA) approval.
A spokeswoman told us "The site currently produces Benlysta for intravenous use. If belimumab for subcutaneous use is approved, the site will have the capability to produce the bulk drug substance for both."
According to GSK figures, the product generated revenue of $377m in the US last year, which is up 18% on the 2015.
No new jobs
The expansion is unlikely to create new jobs according to GSK. The spokeswoman told us "We currently employ more than 400 highly-skilled scientists, engineers, and manufacturing and quality professionals among other specialists at the Rockville facility.
"We don’t anticipate new full-time roles at GSK as a result of this expansion. However, there may be contracts awarded to local construction companies."
News of the expansion comes months after GSK announced the opening of a $50m vaccine R&D facility at the Rockville campus.