Inclusion Criteria:

• Voluntarily provide written informed consent prior to conduct of any study-related procedures
• Completed 24 weeks of treatment in PRO-805
• Deemed appropriate for entry into this extension study by the Investigator
• Females of childbearing potential and fertile males must use a reliable means of contraception

Exclusion Criteria:

• Presence of aspartate aminotransferase (AST) levels ≥ 3 X upper limit of normal and/or alanine aminotransferase (ALT) levels ≥ 3 X upper limit of normal and/or total bilirubin ≥ 1.5 X upper limit of normal and/or creatinine ≥ 1.5 X upper limit of normal
• Current diagnosis of chronic pain requiring opioids for treatment
• Pregnant or lactating females
• Current use of agents metabolized through cytochrome P450 3A4 (CYP 3A4) such as azole antifungals (e.g., ketoconazole), macrolide antibiotics (e.g., erythromycin), and protease inhibitors (e.g., ritonavir, indinavir, and saquinavir)
• Current anti-coagulant therapy (such as warfarin) or an INR > 1.2
• Current use of benzodiazepines other than physician prescribed use
• Significant medical or psychiatric symptoms, cognitive impairment, or other factors which in the opinion of the Investigator, would preclude compliance with the protocol, patient safety, adequate cooperation in the study, or obtaining informed consent
• Concurrent medical conditions (such as severe respiratory insufficiency) that may prevent the patient from safely participating in study; and/or any pending legal action that could prohibit participation and/or compliance in study