Geographic atrophy associated with intermediate macular degeneration. | Courtesy of National Eye Institute, National Institutes of Health.

Shares of Louisville-based Apellis Pharmaceuticals plunged 17 percent Thursday after the bio startup said that some patients suffered inflammation in late-stage clinical trials for a drug that combats a blinding disease.

The company said it has reverted to nonhuman studies to confirm its suspicion that the inflammation is related to a manufacturing problem — not to the drug itself — and hopes to have confirmation by late November.

Shares fell as much as 19 percent early Thursday before recovering slightly. They closed at $13.86, down about 17 percent.

In a filing with the Securities and Exchange Commission, Apellis said that it had “voluntary implemented a temporary pause in dosing” after finding that eight patients “from a single manufacturing lot” of the drug, APL-2, had developed a noninfectious inflammation.

“Inflammation in seven of the eight patients has completely resolved and the other is expected to resolve,” the company said.

The company said that based on an initial preliminary toxicity analysis and the drug’s safety history, it “believes that the cause of inflammation is isolated” to the manufacturing lot.

“At this time, all indications are that the cause of inflammation was isolated to a single lot of APL-2, which we have eliminated from the trial inventory,” CEO Cedric Francois told Insider in an emailed statement.

Phase III trials of APL-2 are continuing with a different lot.

Apellis said that after reviewing the developments with the Data Safety Monitoring Board, an independent review body that focuses on the safety of trial participants, it has “commenced a series of confirmatory nonhuman studies,” which it expects to complete late next month.

If those studies confirm that the inflammation was related to manufacturing, Apellis said that expects the incidents to have no impact on its initial timeline of the drug trial.

The bio startup had said in July that the Food and Drug Administration had given APL-2 its Fast Track designation, which indicates an expedited review and is given to drugs that treat serious conditions and fill an unmet medical need.

APL-2 targets geographic atrophy, an age-related form of macular degeneration, a blinding disease that “makes it difficult for patients to recognize faces, read, drive a car and go about their daily lives,” Francois has said.

“Today, about 1 million Americans live with GA, and unfortunately, there are no approved treatments,” Francois told Insider Thursday. “Apellis is committed to finding a safe, effective treatment to help these patients retain their vision and maximize their quality of life and workplace productivity.”

Phase 3 clinical trials of the drug commenced last month. Phase 3 trials typically last one to four years and involve 300 to 3,000 volunteers who have the disease. The trials are to determine the drug’s effectiveness and side effects. About 25 to 30 percent of drugs move on to Phase 4, the final phase of clinical trials.

UPDATE: This story was updated with the latest share price information and comments from Apellis CEO Cedric Francois.