Efficacy and Safety Study of BIIB074 in Participants With Small Fiber Neuropathy

A Phase 2 Placebo-Controlled, Double-Blind, Enriched Enrollment Randomized Withdrawal Study to Evaluate the Efficacy and Safety of BIIB074 (Vixotrigine) in Treating Pain Experienced by Subjects With Confirmed Small Fiber Neuropathy That is Idiopathic or Associated With Diabetes Mellitus

The primary objective of this study is to evaluate the efficacy of BIIB074 in treating pain experienced by participants with confirmed small fiber neuropathy (SFN) that is idiopathic or associated with diabetes mellitus. A secondary endpoint that relates to the primary objective is the change from Randomization to Week 12 of the double-blind period in mean average daily pain score.

The secondary objectives of this study are to evaluate the effect on worst pain, neuropathic pain quality, sleep interference due to pain, patient global impression, use of rescue medication, and SFN symptoms in participants treated with BIIB074; to investigate the safety and tolerability of BIIB074 in participants with SFN; and to characterize the pharmacokinetics (PK) of BIIB074 in participants with SFN.

Key Inclusion Criteria:

1. This study will be conducted in subjects who have had a diagnosis of at least probable SFN, length-dependent distribution, for 6 months and ≤10 years prior to screening, defined as a history of the symptoms and clinical signs based on discussions at the ACTTION CONCEPPT meeting on diagnosis of SFN, Washington, DC March 2018, and confirmed by intraepidermal nerve fiber density (IENFD) values, and weekly mean average daily pain (ADP) score of ≥5 and ≤9 on an 11-point Pain Intensity Numeric Rating Scale (PI-NRS) over the last 7 days of prior to the Screening visit.
2. In addition to these criteria, subjects with diabetes will be required to have HbA1c ≤11%, treated with oral hypoglycemics and/or subcutaneous insulin or diet, no evidence of ulcers, advanced retinopathy (defined as greater than State 3 [moderate non-proliferative diabetic retinopathy]) (DCCT/EDIC Research Group 2017), severe nephropathy, or clinically significant obstructive atherosclerotic disease or current class IV heart failure to be eligible for the study.

Key Exclusion Criteria:

1. Previous exposure to BIIB074 (formerly known as CNV1014802 or GSK1014802).
2. Use of capsaicin patch within 3 months prior to Screening.
3. Unable or unwilling to discontinue concomitant medications for SFN pain prior to Day 1.
4. Unable or unwilling to comply with the prohibited concomitant medication restrictions, including but not limited to UDP-glucuronosyltransferase (UGT) inducers and inhibitors, monoamine oxidase inhibitors (MAOIs), and Nav blockers.
5. Use of over-the-counter medications, vitamin and mineral supplements, herbal remedies (including St. John's wort), dietary supplements, or foods (including grapefruit juice) that affect and UGTs.
6. Unable or unwilling to discontinue medications that are P-glycoprotein substrates with a narrow therapeutic index, including but not limited to digoxin.
7. History of hemophilia or Von Willebrand's disease, or use of anticoagulants that may result in bleeding risk during the skin biopsy.
8. Any contraindication, as determined by the Investigator, to performing a skin biopsy for intraepidermal nerve fiber analysis.

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