Sept 1 (Reuters) - The U.S. drugs regulator on Wednesday asked Pfizer Inc, Eli Lilly & Co and AbbVie Inc to include information about risks of serious conditions and death from the use of a class of treatments known as JAK inhibitors. The warnings stem from the U.S. Food and Drug Administration’s review of Pfizer’s arthritis drug Xeljanz after initial results from a February trial showed an increased risk of serious heart-related problems and cancer with the drug. AbbVie shares fell 7%, while Pfizer and Eli Lilly were slightly lower. The companies did not immediately respond to a request for comment. JAK inhibitors block inflammation-causing enzymes, known as Janus kinases, and target autoimmune diseases such as rheumatoid arthritis and ulcerative colitis. The FDA said the Lilly drug Olumiant and AbbVie’s Rinvoq have similar operating mechanisms, leading to the possibility of risks seen in the Xeljanz safety trial. Incyte Corp’s Jakafi and Bristol Myers Squibb’s JAK inhibitor Inrebic will not need warnings as they are not approved to treat inflammatory conditions, the agency said. (Reporting by Manas Mishra in Bengaluru; Editing by Aditya Soni) Our Standards: The Thomson Reuters Trust Principles.