Pfizer failed to properly investigate reports of malfunctioning EpiPens, including cases that resulted in severe illness or death, the U.S. Food and Drug Administration said in a warning letter issued earlier this week.
In the warning letter, the FDA said that despite receiving numerous complaints, Meridian Medical Technologies -- a unit of Pfizer -- did not adequately investigate problems with a critical part of the EpiPen, the mechanism that makes it fire and deliver the correct dose of epinephrine, The New York Times reported.
"Our own data show that you received hundreds of complaints that your EpiPen products failed to operate during life-threatening emergencies, including some situations in which patients subsequently died," the FDA said in the letter.
The agency did not provide the number of patient deaths reported.
In a statetment, Pfizer spokeswoman Kim Bencker said the company was "very confident in the safety and efficacy of EpiPen products being produced at the site" and noted that it has distributed more than 30 million EpiPens since 2015, The Times reported.
"It's not unusual to receive product complaints, especially when the product is frequently administered by non-medically trained individuals," according to Bencker.
"We currently have no information to indicate that there was any causal connection between these product complaints and any patient deaths," she added.