April 29 (Reuters) - Regeneron missed Wall Street estimates for first-quarter results on Tuesday, hurt by waning demand for its blockbuster eye disease drug Eylea, sending the company's shares tumbling 9.4% in morning trading.

The drugmaker has been grappling with stiff competition for Eylea from cheaper versions and rivals, including Roche's Vabysmo.

Regeneron said Eylea sales were also hit by lower wholesale inventory levels at the end of the quarter and a lower net selling price.

Last week, the U.S. Food and Drug Administration also declined to approve a pre-filled syringe version of Eylea HD, the higher-dose version of the drug, citing issues with a third-party supplier, Regeneron said on Tuesday.

"We expect a negative reaction as frustrations mount with the company's regulatory execution," Evercore ISI said.

On an adjusted basis, Regeneron earned $8.22 per share in the first quarter, below the average analyst estimate of $8.82, according to data compiled by LSEG.

U.S. sales of Eylea, jointly developed with Bayer, fell 26% to $1.04 billion. Analysts had expected $1.18 billion, according to BMO Capital markets.

Eylea is used to treat eye diseases such as macular degeneration, macular edema and retinopathy.

Regeneron's total revenue for the quarter came in at $3.03 billion, below expectations of $3.27 billion, according to data compiled by LSEG.

Sales of the company's top-selling anti-inflammatory drug Dupixent, made jointly with France's Sanofi, rose 19% to $3.67 billion, compared with estimates of $3.7 billion.

Sanofi last week beat first-quarter profit estimates driven by strong demand for Dupixent. Sanofi records Dupixent sales, and profits are split equally between the two companies.

"While Eylea will remain a point of uncertainty ... we expect Dupixent strength should at least partially offset incremental Eylea headwinds," according to J.P.Morgan analysts.

Regeneron's skin cancer treatment Libtayo brought in sales of $285 million, below estimates of $340.5 million.