Dose Response Study of EMA401 in Patients With Post-herpetic Neuralgia (PHN)

Inclusion Criteria: * At the time of Screening, must have had documented diagnosis of PHN (ICD-10 code B02.29), defined as pain in the region of the rash persisting for more than 6 months after onset of herpes zoster rash. * Assessed as suffering from moderate to severe neuropathic pain across the Screening epoch (NRS ≥ 4). * Patients must have had documented past and/or ongoing inadequate treatment response (having insufficient pain relief with treatment or inability to tolerate) to at least 2 different prescribed therapies commonly used to treat and considered effective by the Investigator for the treatment of PHN. * Patient must have been willing to complete daily eDiary Exclusion Criteria: * History or had current diagnosis of electrocardiogram (ECG) abnormalities indicating significant risk of safety for patients participating in the study * Had a major depressive episode within 6 months prior to Screening and/or a history of diagnosed recurrent major depressive disorder according to Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-V) diagnostic criteria * Women of child-bearing potential, defined as all women physiologically capable of becoming pregnant. * Had evidence of significant renal insufficiency or pre-existing liver condition * Had platelets ≤ 100 x 10\^9/L, or neutrophil count \< 1.2 x 10\^9/L (or equivalent), hemoglobin ≤ 100 g/L for women or hemoglobin ≤ 110 g/L for men. * Patients who had a known diagnosis of diabetes and are stabl…