Dec 28 (Reuters) - The U.S. Food and Drug Administration on Wednesday approved TG Therapeutics Inc's drug for patients with relapsing forms of multiple sclerosis, pitting it against rivals from Roche and Novartis, according to the health regulator's website. (Reporting by Sriparna Roy, Khushi Mandowara and Raghav Mahobe in Bengaluru; Editing by Anil D'Silva)