What happened

Regeneron Pharmaceuticals (REGN -1.75%), a large-cap biotechnology company, is under heavy pressure today. Specifically, the biotech's stock was down by an unsightly 6.5% on heavy volume as of 12:19 p.m. ET Thursday afternoon. 

Regeneron's shares are moving southward in response to lower-than-expected sales of its flagship eye-care treatment, Eylea, during the first quarter of 2023. Eylea is indicated for serious eye conditions such as age-related macular degeneration (AMD) and diabetic macular edema (DME). 

So what

In the first quarter, Regeneron reported a 6% dip in year-over-year U.S. sales for the eye-care drug, reflecting increasing competition from newer rivals like Roche's Vabysmo.

On the bright side, Regeneron and partner Bayer currently have a regulatory filing under review with the Food and Drug Administration (FDA) for a longer-acting formulation of Eylea as a treatment for both AMD and DME. The FDA's target action date for the filing is presently June 27. If approved, Regeneron and Bayer plan to immediately launch this higher-strength version of the drug. 

Despite this mid-single-digit decline in Eylea sales, Regeneron still posted a healthy 7% rise in quarterly sales to $3.16 billion, relative to the same period a year ago. The biotech's top-line growth was fueled in part by the rapidly rising sales of the Sanofi-partnered inflammatory medication, Dupixent. A $222 million collaboration payment from Roche for the COVID-19 medicine Ronapreve also helped to boost the biotech's top line during the quarter. 

Now what

Is Regeneron stock a buy on this dip? I think so. The company remains on track to post a healthy 10.8% rise in annual sales over the course of 2023 and 2024. As such, this pullback is likely to be temporary.