Subjects who satisfy entry criteria at Screening will enter the Washout Phase, discontinuing their current nonsteroidal anti-inflammatory drug (NSAID) therapy.
Up to 220 subjects who fulfill flare (and other entry) criteria will be randomized to gefapixant or placebo.
Subjects will complete Treatment Visits 1, 2, 3, and 4 weeks after starting study drug. At each Treatment Visit, subjects will undergo efficacy assessments and safety procedures. During the Washout and Treatment Phases subjects will complete the 'average pain' Numeric Pain Rating Scale (NPRS) and count of rescue medication used for the preceding 24 hours.
Subjects will return 2 weeks after their last Treatment Visit (for a Follow-Up Visit).
