A Study of RTA 901 (BIIB143) in Participants With Diabetic Peripheral Neuropathic Pain

Run-in Inclusion Criteria:

• Diagnosis of type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM) atleast 1 year prior to Screening

• Clinical diagnosis of DPNP defined as symptomatic distal symmetric polyneuropathy (secondary to diabetes) in the lower extremities, which may include symptoms of painthat is burning, lancinating, tingling, or shooting (electric shock-like). Pain inthe lower extremities may occur with paresthesia or dysesthesia (unpleasantsensations of burning). Neuropathic pain may be accompanied by an exaggeratedresponse to painful stimuli (hyperalgesia) and pain evoked by light touch orcontact, eg, with socks, shoes, and bedclothes (allodynia);

• NPRS pain intensity score ≥ 4 on an 11-point scale at Screening

• A score ≥ 2.5 on the Michigan Neuropathy Screening Instrument (MNSI) Part B

Run-in Exclusion Criteria:

• Has neuropathy from a cause other than T1DM or T2DM

• Has a condition other than DPNP that could confound the assessment of pain (eg,fibromyalgia or regional pain caused by lumbar or cervical compression);

• Diabetic foot ulceration or infection within 90 days prior to Screening

• Prior participation in a study with RTA 901;

NOTE: Other protocol-defined Inclusion/Exclusion criteria may apply.