Eli Lilly and Co. said it discontinued a trial of an experimental rheumatoid arthritis drug for lack of efficacy.

The trial, in the last stage of three generally required for regulatory approval, is one of three studies of tabalumab in rheumatoid arthritis, the Indianapolis-based company said Thursday in a prepared statement. The decision wasn’t based on safety concerns, Lilly said.

The company is still weighing the drug in the two other late-stage studies, and is holding off on enrolling new patients until more analyses are finished early next year. Those studies are being done in different populations of patients, Lilly said. The company is still evaluating tabalumab in systemic lupus erythematosus.

“The results of this study were unexpected given the data generated in earlier Phase II clinical studies of tabalumab,” Eiry Roberts, Lilly’s vice president of autoimmune product development, said in the statement. “We remain committed to patients with rheumatoid arthritis and lupus and will move rapidly to evaluate the impact of these data on the overall tabalumab clinical development program.”

Lilly said it expects to take a pretax charge of $20 million to $35 million in the fourth quarter, or about 2 cents a share after tax. The company’s 2012 forecast is unchanged, it said.

Two other companies reported discouraging trial results for a rheumatoid arthritis drug on Thursday. AstraZeneca PLC and Rigel Therapeutics Inc. said their drug fostamatinib did not work as well as Abbott Laboratories Inc.'s Humira in a mid-stage clinical trial. AstraZeneca is running a larger trial of fostamatinib and expects to get results in early 2013.

Rigel's stock plunged 34.6 percent, to $5.51 per share, Thursday on the news.

Humira is the leading rheumatoid arthritis drug by sales, bringing in about $9 billion in annual revenue.

Rheumatoid arthritis is a major area of research for drug companies because it is a chronic condition, meaning patients will likely take the drugs regularly for a long time. In November, the Food and Drug Administration approved a new treatment for the disease, Pfizer Inc.'s twice-a-day pill Xeljanz.

Shares of Lilly lost 77 cents, to $48.23 each, on Thursday. AstraZeneca shares fell 2.9 percent, to $47.46, and shares of Abbott Laboratories lost 69 cents, to $65.32.