Shares of Epipen manufacturer Mylan dropped Tuesday afternoon following the release of a letter to the firm from the U.S. Food and Drug Administration, which raised concerns about quality controls at one of Mylan's manufacturing plants in India.
"Your quality system does not adequately ensure the accuracy and integrity of data to support the safety, effectiveness, and quality of the drugs you manufacture," the FDA said in its letter to Mylan. These conclusions were drawn after the FDA launched an investigation into Mylan's Nashik facility, the group said.
Mylan's stock fell more than 2 percent following this news Tuesday afternoon and is down nearly 16 percent over the past year.
In a statement to CNBC, a Mylan spokeswoman said Tuesday: "Mylan received a warning letter with two observations from the U.S. Food and Drug Administration (FDA) and we are working closely with FDA to respond to and address the issues raised in the letter as comprehensively and expeditiously as possible."
Production from Mylan's Nashik site continues uninterrupted at this time, the spokesperson also noted. The facility produces antiretroviral therapies used to treat HIV.
The FDA further explained in its letter several violations in the Nashik plant, including a failure to "thoroughly investigate" unexplained discrepancies in drug batches, citing examples of "missing, deleted, and lost data."
"Until you correct all violations completely and we confirm your compliance with CGMP, FDA may withhold approval of any new applications or supplements listing your firm as a drug manufacturer," the regulatory group wrote in its note published Tuesday.
According to Reuters, Mylan has nine independent sites, including this facility, that produce and supply antiretroviral therapies.
In 2015, the FDA sent a warning letter to Mylan expressing concerns over quality controls at three of the firm's facilities in Bangalore, the capital of India's southern Karnataka state.
— Reuters contributed to this report.