UPDATE 2-AbbVie's rheumatoid arthritis drug succeeds in late-stage trial

* AbbVie shares rise as much as 2.1 pct

* Study data comes 2 months after FDA rejection of baricitinib

* Upadacitinib could edge out baricitinib on efficacy-analyst (Adds analyst comment; updates shares)

June 7 (Reuters) - U.S. drugmaker AbbVie Inc said on Wednesday its rheumatoid arthritis drug was found to be superior to a placebo in a late-stage study involving patients that have not responded adequately to standard treatments.

Two doses of the drug, upadacitinib, were tested against a placebo in the 12-week study in patients with moderate-to-severe rheumatoid arthritis, a chronic inflammatory disease in which the immune system attacks the tissues of the joints, causing inflammation, pain, joint damage and disability.

Upadacitinib is a once-daily pill belonging to a class of drugs known as Jak inhibitors, which block inflammation-causing enzymes known as Janus kinases.

Jak inhibitors compete with injected biologics, including Amgen Inc's Enbrel.

The late-stage data comes almost two months after the U.S. Food and Drug Administration (FDA) declined to approve Eli Lilly and Co and partner Incyte Corp's rheumatoid arthritis drug, baricitinib.

If approved, upadacitinib could help AbbVie lower its reliance on its flagship rheumatoid arthritis treatment, Humira, which is also the world's top selling drug.

The FDA has already approved a biosimilar version of Humira, made by Amgen, but AbbVie is trying to block its launch, contending that Humira's patents should protect it until at least 2022.

In the upadacitinib trial, 64 percent of patients on a 15-milligram dose and 66 percent on a 30-milligram dose experienced a 20 percent reduction in symptoms on a commonly used rheumatoid arthritis scale, compared with 36 percent of patients on the placebo meeting the main goal of the study.

It is possible that upadacitinib might edge out Lilly and Incyte's baricitinib on efficacy as more data is released, Jefferies analyst Jeffrey Holford said.

AbbVie is also evaluating upadacitinib for several other conditions, including psoriatic arthritis, Crohn's disease and ulcerative colitis. Holford estimated peak sales of $3.5 billion for the drug across all diseases.

The company is also running five more upadacitinib trials in various rheumatoid arthritis populations. Data from those trials is expected over the coming months.

More than 23 million people suffer from rheumatoid arthritis. Current treatments include non-steroidal anti-inflammatory drugs as well as older drugs such as methotrexate.

AbbVie's shares rose as much as 2.1 percent to $69.32 in morning trading on Wednesday. (Reporting by Divya Grover in Bengaluru; Editing by Sai Sachin Ravikumar)