Mylan Pharmaceuticals has come under intense fire for massive price hikes of EpiPens over the last week, facing scrutiny from lawmakers and industry groups. It is less well known, however, that while Mylan markets and prices the drug, Pfizer Inc. actually manufactures the drug and has seen increased revenues from EpiPens over the last few years.

The financial relationship between the two drug companies is unclear, and Pfizer declined to elaborate. Mylan did not respond to a request for further comment about EpiPens or how the two companies divide revenues.

“Meridian Medical Technologies is the contract manufacturer of EpiPen and takes great pride being able to supply a high quality and life-saving product. The terms of our supply agreement are confidential,” said Rachel Hooper, a Pfizer spokeswoman. Meridian Medical Technologies is a Pfizer subsidiary.

The EpiPen outrage centers around a 400 percent hike for the dispenser, used for emergency allergic reactions, since 2009, even though the product remains unchanged. It now costs as much as $600 for a pack of two EpiPens, which must be replaced every 12 to 18 months.