Merck Sharp & Dohme Corp. has filed an IPR petition on U.S. Patent No. 6,331,415. This patent has been challenged several times over the past year with mixed results: IPR2015-01624 (instituted); IPR2016-00383 (not instituted); IPR2016-00460 (joined with IPR2015-01624); and IPR2016-0710 (petition pending).