Shares of Regeneron Pharmaceuticals Inc. (REGN) - Get Report fell 4.2% on Friday, June 23, to $502.60 on reports questioning how far the shares could continue rising. As of the close on Thursday, June 22, the shares had climbed from $456.22 on June 16 to $504.60 due to the strong launch for Dupixent Regeneron's treatment for severe atopic dermatitis. Sales for treating U.S. adult are predicted to be $951 million by 2023. It is also being tested as an asthma treatment.

The main headwind for Regeneron is that Swiss pharma giant Novartis could soon be a rival to the eye drug that drives most of Regeneron's revenue. Novartis released data from its RTH258 clinical trials illustrating that RTH258 does not need to be injected as often as Regeneron's counterpart, Eylea, to treat neovascular AMD, a leading cause of vision loss.

Shares of Amgen Inc. (AMGN) - Get Report fell 1% after the FDA rejected Pfizer Inc.'s (PFE) - Get Report marketing application for Pfizer's Epogen biosimiar. The rejection was related to concerns about Pfizer's McPherson, KS facility, a potential manufacturing site for the product.