Inclusion Criteria:

• Male or female age 18 to 75 years
• Patients with type 1 or type 2 diabetes mellitus
• DPN as determined by the investigator based on clinical history, clinical examination, and assessment of signs and symptoms
• Stable diabetic control over the preceding 3 months, as determined by the investigator based on available medical information (e.g., hemoglobin A1c [HbA1c] and/or blood glucose levels)
• HbA1c ≤ 12 % at the Screening visit
• Pain persisting for more than 3 months and less than 5 years
• Completion of 3 daily pain intensity reports (using the 11-point NPRS) over the 3 days immediately preceding the day of randomization
• Pain intensity (NPRS) score of ≥ 5 for all 3 of the 3 days immediately preceding the day of randomization
• Completed a washout (before first NPRS assessment) of at least 7 days for any of the following medications: α2-δ antagonists (e.g., gabapentin, pregabalin), opiate analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), topical lidocaine, anti-epileptic drugs, serotonin and norepinephrine reuptake inhibitors (SNRIs) (e.g., duloxetine), tricyclic antidepressants prescribed for pain, skeletal muscle relaxants, orally administered steroids, capsaicin, mexiletene, centrally acting analgesics (dextromethorphan, tramadol), alpha lipoic acid, and any supplement or herbal product used to treat DPN symptoms
• Women must be neither pregnant nor lactating. Women of childbearing age must have a confirmed negative pregnancy test and must practice medically acceptable methods of contraception throughout the trial and for at least 30 days after the last dose of study drug
• Male subjects and/or their female partners must be using medically acceptable methods of contraception for the entire duration of the study, and for at least 90 days after the last study drug dose
• Evidence of a personally signed and dated informed consent document indicating that the subject has been informed of all pertinent aspects of the study
• A willingness and ability to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures

Exclusion Criteria:

• Age younger than 18 years or older than 75 years
• Are pregnant or breast feeding
• Female patients of childbearing potential unwilling to use a medically acceptable form of contraception (i.e., hormonal birth control, intrauterine device [IUD], double barrier [male condom or female condom with a diaphragm], or a barrier method plus a spermicidal agent [contraceptive foam, jelly, or cream]) Female patients are considered to be of childbearing potential unless they have been postmenopausal for at least 1 year, are biologically sterile, or are surgically sterile (history of hysterectomy, bilateral oophorectomy, or bilateral tubal ligation.
• Male patients (and/or their female partners) unwilling to use a medically acceptable form of contraception during participation in the study and for at least 90 days after the last dose of study drug. Medically acceptable forms of contraception are hormonal birth control, intrauterine device (IUD), double barrier (male condom or female condom with a diaphragm), or a barrier method plus a spermicidal agent (contraceptive foam, jelly, or cream)
• Treatment with local anesthetic nerve blocks within the last 30 days before the Screening visit
• Other severe pain which may impair the self-assessment of pain due to DPN
• Participation in another study within 30 days before the Screening visit and/or during study participation
• History of drug or alcohol abuse within the past 2 years
• Creatinine clearance < 50 mL/min at the Screening visit
• Malignancy other than basal cell carcinoma and carcinoma in situ within the past 2 years
• History of chronic hepatitis B or C, hepatitis within the past 3 months before the Screening visit, or any history of human immunodeficiency virus (HIV) infection
• Clinically significant hepatic, respiratory, hematological, cardiovascular, renal, or neurological disease, with the exception of diabetic peripheral neuropathy
• Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 2.5 times higher than the upper limit of the laboratory normal reference range at the Screening visit
• ECG with a QTcB > 470 ms at the Screening visit or at Baseline (if at either the Screening visit or Baseline the ECG shows a QTcB > 470 ms, then the investigator may immediately repeat the ECG twice and the QTcB value for inclusion/exclusion purposes will be determined by calculating the average of the 3 readings)
• Immunocompromised state
• Other severe acute or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation