Amgen Stock After Hours (AMGN) on Dec. 22, 2025: FDA Clears New Prolia/Xgeva Biosimilars, Fitch Upgrades Credit — What to Know Before the Dec. 23 Open
Amgen Inc. ended Monday, December 22, 2025, modestly higher, but the more important story for Tuesday’s open is what hit after the closing bell: fresh FDA approvals for new denosumab biosimilars that reference Amgen’s blockbuster bone-drug franchises Prolia and XGEVA—plus a credit-rating upgrade from Fitch that underscores improving balance-sheet flexibility.