(Corrects paragraph 3 to clarify that Xeljanz is the only U.S.-approved JAK inhibitor)
* Upadacitinib, a JAK inhibitor, more effective than a placebo
* FDA had rejected a rival JAK inhibitor drug 2 months back
* Drug could help lower AbbVie's reliance on Humira
* AbbVie shares rise as much as 2.1 pct to 22-month high
By Divya Grover
June 7 (Reuters) - AbbVie Inc said on Wednesday its oral rheumatoid arthritis drug succeeded in a late-stage study on patients who had not adequately responded to standard treatments.
The drug, upadacitinib, is a once-daily pill belonging to a class of drugs known as JAK inhibitors, which block inflammation-causing enzymes called Janus kinases.
Pfizer Inc's Xeljanz is the only U.S.-approved JAK inhibitor for rheumatoid arthritis – a chronic inflammatory disease in which the immune system attacks tissues in the joints, affecting more than 23 million people.
AbbVie's success comes almost two months after the U.S. Food and Drug Administration rejected baricitinib, a rival JAK inhibitor developed by Eli Lilly and Co and Incyte Corp .
If approved, upadacitinib could help AbbVie lower its reliance on its flagship rheumatoid arthritis drug Humira – the world's top selling medicine that will soon face competition from biosimilars in the United States.
AbbVie's shares were up 1.4 percent at $68.81 on Wednesday afternoon. They earlier hit a session high of $69.32, their highest since August 2015.
In AbbVie's 12-week study on upadacitinib, two doses of the drug were tested against a placebo on patients with moderate-to-severe rheumatoid arthritis.
AbbVie said 64 percent of patients given a 15-milligram dose and 66 percent of patients given a 30-mg dose experienced a 20 percent reduction in symptoms, measured using a commonly used rheumatoid arthritis scale.
The company said only 36 percent of patients given a placebo experienced a comparable drop in symptoms, meaning upadacitinib cleared the trial – the first of six testing the drug on patients with various cases of rheumatoid arthritis.
As data from the other trials comes in, upadacitinib might prove to be more effective than Lilly and Incyte's baricitinib, Jefferies analyst Jeffrey Holford said.
Rheumatoid arthritis is currently treated with older drugs such as methotrexate, Pfizer's JAK inhibitor Xeljanz as well as injected biologics such as Amgen Inc's Enbrel and AbbVie's Humira.
Humira generated more than $16 billion in sales last year, but competition is looming. AbbVie is trying to block the launch of an FDA-approved biosimilar, made by Amgen, arguing that its patents on Humira offered protection until at least 2022.
AbbVie is also evaluating upadacitinib for several other autoimmune conditions, including psoriatic arthritis, Crohn's disease and ulcerative colitis.
Holford estimated peak sales of $3.5 billion for the drug across all diseases. Pfizer's Xeljanz generated sales of $927 million last year. (Reporting by Divya Grover in Bengaluru, additional reporting by Natalie Grover; Editing by Sai Sachin Ravikumar and by Savio D'Souza)