(2R,6R)-Hydroxynorketamine for the Treatment of Neuropathic Pain

Adult patients (18 to 80 years) with an established diagnosis of chronic (\> 3 month) neuropathic pain (NP) of the extremities will be identified and screened for study inclusion. After informed consent is obtained, subject will be randomized into a (2R,6R)-HNK (H), ketamine (K) or saline (S) infusion groups for each of the study drug administration periods. The group sequences for the infusions will be: KSH, HSK, KHS, SKH and HKS and each group will contain 5 subjects at each sequence. Study subjects will be evaluated for at least 7 days prior to the first treatment and for 35 days following each treatment. Researchers involved in the subject's care and assessments will be blinded to group allocation. Safety will be assessed throughout the study. Baseline safety assessments will include height, body mass index (BMI), weight, temperature, medical, visual and ocular history, physical examinations, and vital signs (VS). Prior to study commencement and 28 days after each drug infusion a blood chemistry panel, liver function tests (LFT), a complete blood count (CBC) and a 12-lead electrocardiogram (ECG) will be obtained. A pretreatment quantitative pain evaluation will assess overall pain level, pain tolerance, pinprick hyperalgesia, touch, brush and cold allodynia. Patients will be maintained on their current scheduled analgesic regimen during the study and instructed to use on-demand analgesic only as needed.