There are two parts to this study, each part includes double-blind treatment with either CTP-499 or placebo. Part 1 will evaluate the safety and efficacy of treatment with CTP-499 twice daily for 24 weeks. Part 2 will evaluate the effects of longer term dosing for an additional 24 weeks. Following Part 2, patients will be allowed to participate in an Open Label extension with CTP-499 for a period of an additional 48 weeks.
