Irvine-based Ista Pharmaceuticals Inc.’s has seen the debut of a long awaited generic rival to its Xibrom drug for cataract surgery patients.

Pennsylvania’s Mylan Inc. has started selling a generic version of the drug to treat inflammation and pain after cataract surgery.

In March, Ista asked the Food and Drug Administration to reject a generic version of Xibrom, citing safety concerns.

Competitive issues also likely were a factor.

The company also is expected to see generic competition from Switzerland’s Alcon Inc.

Ista’s shares closed down about 3% trading to a market value of some $335 million.

The company has prepared for generic competition.

In February, Ista stopped shipping Xibrom, which is used twice daily, after getting approval for a once-daily version of the drug called Bromday.

The company has been able to switch doctors from Xibrom to Bromday, according to Chief Executive Vince Anido.

Xibrom has been Ista’s historical flagship drug, accounting for about 70% of the company’s annual sales of more than $150 million last year.