What happened

Shares of Regeneron Pharmaceuticals Inc. (NASDAQ:REGN), the biotech that markets vision-loss treatment Eylea, fell 12.6% in February according to data from S&P Global Market Intelligence. Trial results unveiled last month suggest the company's flagship drug could face fiercer competition than just Lucentis in the years ahead.

So what 

U.S. sales of Eylea rose 11% to $3.7 billion last year. Although those numbers are still moving in the right direction, Regeneron depends on domestic sales of the pricey eyeball injection for 63% of its total revenue. That's why some less-than-positive Eylea related news was enough to pressure the stock.

Person making an angry gesture in front of stock charts.

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Eylea competes with Lucentis from Roche (NASDAQOTH:RHHBY), and it looks like the Swiss drugmaker has another contender ready for late-stage testing. Last month, Roche showed mid-stage results from a dose-determination study with the bispecific antibody known as RG7716. The treatment led to an average improvement of 13.9 eye chart letters from baseline, at the highest dose tested, versus 10.3 letters among patients treated with Lucentis.

Now what

Before you get too worried about RG7716, it's important to realize Eylea hasn't had much trouble competing with Lucentis in the U.S. market. Despite a five-year head start, sales of Roche's injection rose just 1% last year to around $1.5 billion.

Roche still needs to meet with regulators to discuss a pivotal trial design, which means RG7716 won't even begin to threaten Eylea for at least a couple years. By then, royalties from Sanofi (NYSE: SNY) for sales of Praluent, Kevzara, and Dupixent could more than offset any losses.

Cory Renauer has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.