The U.S. Food and Drug Administration (FDA) is taking Pfizer Inc. (NYSE:PFE) to task for allegedly not properly investigating cases of EpiPen failure.

A letter from the FDA accuses Pfizer Inc. of ignoring cases in which EpiPens didn’t operate properly. It claims that some of these cases resulted in death due to the proper amount of epinephrine not being distributed to treat an allergic reaction.

The FDA’s letter specifically calls out Pfizer Inc. for not investigating a case of EpiPen failure from back in Feb. 1, 2016. This includes identifying a failed EpiPen in a lot and pulling that lot. However, the company didn’t inspect other lots of EpiPen that were made at the same time as that lot.

The FDA points to a case of EpiPen failure in April of 2016. Pfizer Inc. investigated the incident and found that the EpiPen had the same fault as the one from February. However, it closed the investigation and said it had no plans for market action. A supplier for the company was still investigating issues with these parts at this time.

“Your response is inadequate,” the FDA says in its letter to Pfizer Inc. “You did not explain why your own investigations failed to identify the scope and frequency of the (b)(4) component defect, or why you had previously concluded that this component defect occurred too infrequently to warrant a market action.”

The FDA is giving Pfizer Inc. 15 days to respond to its letter. It wants to know how the company has taken action to resolve the issues it found in its investigation at a Meridian facility. If a letter isn’t sent within this time period, the company must provide a reason for delay and a timeline for when it will have a response ready.

As of this writing, William White did not hold a position in any of the aforementioned securities.