Mylan (NSDQ:MYL) today made public a warning letter that the FDA sent to EpiPen manufacturer, Meridian Medical Technologies.

In the letter, the regulatory agency summarizes “significant violations of current good manufacturing practice requirements for combination products”, including issues relating to quality control procedures, product complaint resolution and design verification.

Among other products, Meridian manufactures Mylan’s EpiPen devices and the FDA scolded the company for not vigorously investigating reports that some of their devices were failing in the field.

“These products are intended to deliver a lifesaving drug (epinephrine) during emergency treatment of serious allergic reactions, including anaphylaxis. If your auto-injectors do not operate as expected and deliver the intended amount of epinephrine drug when deployed in emergencies, patients can die or suffer serious illness,” the agency wrote.

“You failed to thoroughly investigate multiple serious component and product failures for your EpiPen products, including failures associated with patient deaths and severe illness. You also failed to expand the scope of your investigations into these serious and life-threatening failures or take appropriate corrective actions, until FDA’s inspection.

The FDA warned the manufacturer to promptly correct the violations cited in the letter or risk facing legal action.

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