Mylan NV CEO Heather Bresch said there were fluctuations in the supply of its emergency allergy injectable EpiPen due to issues with its manufacturing partner Pfizer Inc.

"We appreciate FDA taking the step to put up on their website, notifying that EpiPens are available, that — and ironically, they have to put that on the shortage, their shortage list to say there's not a shortage," Bresch told analysts on a conference call while discussing the company's first-quarter earnings.

The U.S. Food and Drug Administration has listed Mylan's EpiPen on its drug shortage list adding that while the medication is available, there were intermittent supply constraints due to manufacturing delays from Pfizer's unit Meridian Medical Technologies.

"We've absolutely had fluctuations in that supply. But we continue to see Pfizer being able to step up their ability to supply month over month," Bresch added.