This is an open-label study of DS-5565 in subjects who either completed participation in a preceding Phase 3 study of DS-5565 in fibromyalgia (FM); i.e. DS5565-A-E309 (NCT02146430), DS5565-A-E310 (NCT02187471), or DS5565-A-E311 (NCT02187159) or are de novo subjects. Eligible subjects will be assigned to receive open-label DS-5565 for 52 weeks. All subjects will receive DS-5565 15 mg once daily (QD) for the first three weeks of the treatment period. After three weeks, subjects may be titrated to 15 mg twice daily (BID) based on protocol-specified criteria.

Inclusion Criteria:

• Able to give written informed consent
• Completed participation (i.e. completed the End-of-Tapering visit) in a preceding study of DS 5565 in FM (DS5565-A-E309, DS5565-A-E310, or DS5565-A-E311)
• Women of child-bearing potential (WOCBP) must be using an adequate method of contraception to avoid pregnancy during the study and for 4 weeks after study completion
• Able to complete subject-reported questionaires per the investigator's judgement
• The subject must not have experienced any significant safety issues during the preceding study that, in the investigator's judgment, would adversely impact the subject's well-being in the long-term extension

De Novo Subjects

• Age ≥ 18 years

• Able to give written informed consent

• Able to complete subject-reported questionnaires per the investigator's judgment

• At screening, subjects must meet the 1990 American College of Rheumatology (ACR) criteria for FM, i.e. widespread pain present for at least 3 months and pain in at least 11 of 18 specific tender point sites. In addition, the 2010 ACR criteria must be met:

  • Widespread pain index (WPI) ≥ 7 and symptom severity (SS) scale score ≥ 5, or WPI 3 to 6 and SS scale score ≥ 9
  • Symptoms have been present at a similar level for at least 3 months
  • The subject does not have a disorder that would otherwise explain the pain

• ADPS of ≥ 4 on the 11-point numeric rating scale (NRS) over the past 7 days prior to first dose (based on completion of at least 4 daily pain diaries during the 7-day baseline period)

• Subject must have documented evidence of a fundoscopic examination (with pupil dilation) within 12 months prior to screening or at screening

• Women of child-bearing potential (WOCBP) must be using an adequate method of contraception to avoid pregnancy during the study and for 4 weeks after study completion

Exclusion Criteria:

• Clinically significant unstable neurologic, psychiatric, ophthalmologic, hepatobiliary, respiratory, or hematologic illness or unstable cardiovascular disease (e.g. severe hypotension, uncontrolled cardiac arrhythmia, or myocardial infarction) or any other concurrent disease during the preceding study (for rollover subjects) or within 12 months prior to screening (for de novo subjects) that in the opinion of the investigator would interfere with study participation or assessment of safety and tolerability
• Subjects who are at risk of suicide as defined by their responses to the C-SSRS or in the opinion of the investigator.
• Subjects with severe or uncontrolled depression that, in the judgment of the investigator, makes the subject inappropriate for entry into the study
• Subjects with pain due to other conditions (e.g. DPNP or post-herpetic neuralgia) that, in the opinion of the investigator, would confound assessment or self-evaluation of the pain associated with FM
• Subjects with pain due to any widespread inflammatory musculoskeletal disorder (e.g. rheumatoid arthritis, lupus) or widespread rheumatic disease other than FM.
• Abuse or dependence of prescription medications, street drugs, or alcohol within the last 1 year
• A diagnosis of untreated sleep apnea or initiation of treatment for sleep apnea within the past 3 months
• Known hypersensitivity to α2δ ligands or other components of the study medications
• Pregnancy or breast-feeding, or intent to become pregnant during the study period
• Abnormal investigative tests (i.e. ECGs) and laboratory values judged by the investigator to be clinically significant at the End-of-Treatment visit (Visit - Week 13) in the preceding study (for rollover subjects) or at screening (for de novo subjects), with particular focus on:

For De Novo Subjects Only

• Unable to undergo pre-study washout of prohibited concomitant medications (as listed in Section 5.2.1 of the protocol)
• Current severe or uncontrolled major depressive disorder or anxiety disorders as assessed by the Mini-international Neuropsychiatric Interview (MINI) interview (Version 6.0) at screening are excluded, but mild to moderate major depression or anxiety disorders are permitted provided that the investigator assesses the patient as clinically stable and appropriate for entry into the study
• Any diagnosis of lifetime bipolar disorder or psychotic disorder
• Subject is currently enrolled in or has not yet completed at least 30 days since ending another investigational device or drug study or is receiving other investigational agents
• Subject is an employee of the study center, an immediate family member* of an employee of the study center, or an employee of Daiichi Sankyo, INC Research, or any of the study vendors supporting this study. *(spouse, parent, child, or sibling, whether biological or legally adopted)

De-identified individual participant data (IPD) and applicable supporting clinical trial documents may be available upon request at https://vivli.org/. In cases where clinical trial data and supporting documents are provided pursuant to our company policies and procedures, Daiichi Sankyo will continue to protect the privacy of our clinical trial participants. Details on data sharing criteria and the procedure for requesting access can be found at this web address: https://vivli.org/ourmember/daiichi-sankyo/

Studies for which the medicine and indication have received European Union (EU) and United States (US), and/or Japan (JP) marketing approval on or after 01 January 2014 or by the US or EU or JP Health Authorities when regulatory submissions in all regions are not planned and after the primary study results have been accepted for publication.

Formal request from qualified scientific and medical researchers on IPD and clinical study documents from clinical trials supporting products submitted and licensed in the United States, the European Union and/or Japan from 01 January 2014 and beyond for the purpose of conducting legitimate research. This must be consistent with the principle of safeguarding study participants' privacy and consistent with provision of informed consent.