This study is to Evaluate the Efficacy, Safety, Tolerability, and Pharmacokinetics of SR419 in Patients with Peripheral Neuropathic Pain

This is a three-period, complete crossover, double-blind, randomised, placebo- and active-controlled study to compare the preliminary efficacy of a single dose of SR419 to placebo and active control in patients with peripheral neuropathic pain. The study also aims to evaluate the safety, tolerability, and PK of single doses of SR419 in patients with peripheral neuropathic pain.

Inclusion Criteria:

1. Aged ≥18 years at the time of informed consent.
2. Be diagnosed as suffering from chronic peripheral neuropathic pain, and specifically PHN or DPN.
3. Average daily pain over the last week prior to Screening to be of at least moderate severity (a score of ≥4 on the 11-point numeric rating scale [NRS]) and be of face, limb or torso location.
4. A minimum score of 19 on the pain DETECT questionnaire.

Exclusion Criteria:

1. Being pregnant or lactating at Screening or planning to become pregnant (self or partner) at any time during the study.
2. Prior or ongoing medical conditions, medical history, physical findings, or laboratory abnormality.
3. Known or suspected intolerance or hypersensitivity to any of the study drugs, close related compounds, or any of the stated ingredients.
4. Participants on controlled-release opioids (e.g., morphine) unless on a stable dose of Morphine Equivalent Dose (assessed by the Faculty of Pain Medicine Opioids Calculator) of up to and including 60 mg/day, at the discretion of the Investigator. Participants on instant-release opioids (e.g., codeine, oxycodone) must withhold dosing for 12 hours prior to administration of study drug.
5. Positive testing for human immunodeficiency virus (HIV), hepatitis B surface antigen (HBsAg), or hepatitis C virus (HCV).
6. Creatinine clearance as estimated by estimated glomerular filtration rate (eGFR) <60 mL/min.
7. A history of major psychiatric disorder(s).