IntroductionSodium selenate is a potential disease-modifying treatment for Alzheimer’s disease (AD) which reduces hyperphosphorylated tau through activation of the protein phosphatase 2A enzyme. We have shown sodium selenate to be safe and well tolerated in a 24-week, phase 2a double-blind placebo-controlled randomised controlled trial (RCT), also reporting sodium selenate reduced neurodegeneration on diffusion-weighted MRI. This study assessed the safety and tolerability of chronic sodium selenate treatment (up to 23 months) in patients with AD who had been enrolled in the RCT. Cognitive measures served as secondary outcomes of potential disease-modification.MethodsAn open-label extension study of sodium selenate (10 mg three times a day) in patients with AD who had completed the previous RCT. Twenty-eight patients were enrolled. Patients were regularly monitored for safety, adverse events (AEs) and protocol compliance. Cognitive tests were administered for measures of disease progression.ResultsSixteen patients were discontinued by the sponsor, and 12 discontinued for other reasons. Treatment duration ranged from 6 to 23 months. The majority of AEs were mild (83%), and 33% were treatment-related. Common treatment-related AEs were alopecia (21%) and nail disorder (32%), which both resolved either prior to or following cessation of treatment. Two serious AEs occurred, which were not treatment-related. Alzheimer’s Disease Assessment Scale—Cognitive Subscale 11 score increased 1.8 points over 12 months.DiscussionChronic sodium selenate treatment is safe and well tolerated in patients with AD. Cognitive measures suggest a slowing of disease progression though this could not be confirmed as the study was not controlled. Further research into sodium selenate as a treatment for AD is warranted.