FILE PHOTO: A view shows the U.S. Food and Drug Administration (FDA) headquarters in Silver Spring, Maryland August 14, 2012. REUTERS/Jason Reed/File Photo

By Siddhi Mahatole

(Reuters) -Outlook Therapeutics said on Thursday the U.S. health regulator has again declined to approve its experimental eye drug, citing a lack of substantial evidence of effectiveness and sending its shares plunging 50% to a record low.

The U.S. Food and Drug Administration, in its so-called "complete response letter", recommended the company submit additional efficacy data to support its application for the drug, ONS-5010, for treating patients with wet age-related macular degeneration.

Wet AMD is a chronic eye disorder that causes blurred vision or a blind spot in the patient's visual field, and is the leading cause of blindness among the elderly.

The FDA's decision marks another setback in Outlook's prolonged efforts to enter the market. The company had withdrawn its application for the drug, also called bevacizumab, in 2022, after the FDA requested additional information. A year later, the regulator declined to approve the drug, citing manufacturing issues.

"We intend to meet with the FDA to receive additional clarity on their requirements" to potentially approve ONS-5010, said CEO Bob Jahr, adding that the regulator had not specified whether further clinical trials would be necessary.

Outlook's resubmitted application was based on the results from a key trial conducted to address some of the FDA's previous concerns. In the study, however, ONS-5010 failed to match Roche's drug Lucentis at the eight-week mark.

"The U.S. is a large bevacizumab market, so it does represent a significant setback for the company," said Daniil Gataulin, analyst at Chardan Capital Markets. The company will focus on understanding the additional confirmatory evidence the FDA requires before it makes decisions regarding the next steps, Gataulin said.

Along with Lucentis, Regeneron's Eylea and Roche's Vabysmo are among the approved treatments for wet AMD.

Outlook's drug, under the brand name Lytenava, is approved in the European Union and the UK for the condition.

(Reporting by Unnamalai L, Sriparna Roy and Siddhi Mahatole in Bengaluru; Editing by Mohammed Safi Shamsi and Shilpi Majumdar)