The brand name and generic versions of Mylan’s EpiPen devices are vulnerable to malfunctions that can cause them to work improperly or not at all, according to a federal safety alert issued Tuesday.

The EpiPen and EpiPen Jr. devices, which are commonly used to treat emergency allergic reactions, may have delayed injections or fail to inject properly due to design issues or improper administration by users, the U.S. Food and Drug Administration alert said. The agency was made aware of the issues through a letter Mylan recently sent to healthcare workers warning of the problems. Mylan was recently acquired by drug maker Pfizer but continues to use its name.

In a statement, a Pfizer spokeswoman said the company routinely studies and evaluates data regarding administration of its EpiPen devices.

“Although the issues and use errors identified are low, anything that prevents or delays the administration of the intended dose of epinephrine could result in a high risk to patients,” the Pfizer spokeswoman said. “We encourage healthcare professionals, patients and caregivers to review the letter, which includes available training resources, and regularly read the patient information and instructions for use to be prepared in the event of a life-threatening allergic reaction.”

In the letter to providers, Mylan said a “very” limited number of EpiPen devices have blue safety releases that are slightly raised, which can cause the device to activate prematurely. Mylan informs pharmacists, patients and caregivers to inspect the EpiPen prior to use and to call Mylan for a new device if the malfunction is present. Mylan will provide a new EpiPen at no additional cost.

Mylan also said the EpiPen can malfunction if the blue safety release is removed sideways rather than straight up. Mylan advises not using just your thumb to remove the safety release. Instead, hold the device using both hands and remove the safety by pulling it straight out.

In some instances, the EpiPen may also not slide out of its carrier tubes easily or even at all. The carrier tube is the package that holds the auto-injector. The issue is caused by a “slight deformation,” Mylan said. This issue can affect any EpiPen on the market with an expiration label prior to September 2020. Mylan is telling pharmacists, patients and caregivers to inspect the carrier tubes prior to use to ensure they readily slide out.

In response to the FDA safety alert, Mylan’s stock is down about 4%.