Efficacy and Safety Study of Z160 in Subjects With Postherpetic Neuralgia

Inclusion Criteria: * Provide written informed consent. * Either sex but must be aged \>=18 years. * Diagnosis of PHN as defined by the presence of pain in the area affected by herpes zoster \>=6 months after the herpes zoster skin rash has healed. * Pain score over the last week of \>=3 and \<=8 on the PI-NRS * If female, the subject must be postmenopausal , surgically sterilized for \>=3 months before the screening visit, or agree to use 2 reliable methods of contraception if of childbearing potential. If male, the subject must agree to use condoms. * Willing and able to comply with all study procedures. Exclusion Criteria: * Severe pain caused by diseases other than PHN. * Neurolytic or neurosurgical therapy for PHN within 6 months of screening (subjects who received a spinal cord stimulator implant at least 6 months before screening are eligible, but the settings need to remain stable during the double blind study period without use of a magnet). * History of seizure, excluding pediatric febrile seizures, or currently has seizures. * Stroke or transient ischemic attack (TIA) \<=6 months before the screening visit. * History of or a current diagnosis of schizophrenia or bipolar disorder. * Major depressive disorder or generalized anxiety disorder \<=6 months before the screening visit. Subjects who are on stable doses of selective serotonin uptake inhibitors (SSRIs) for depression (other than major depressive disorder) are eligible for the study. * Clinically significant alcohol or substance dependency \<=1 year before the screening visit * Imminent risk of suicide (positive response to question 4 or 5 on the C-SSRS) or had a suicide attempt within 6 months before the screening visit. * Clinically significant conditions that, in the investigator's opinion, may interfere with the study procedures or compromise the subject's safety. * Malignancy (other than nonmetastatic basal or squamous cell carcinoma of the skin or carcinoma in situ of other organs that was surgically removed \>1 year before screening and has not recurred). * Condition that is known to interfere with the absorption, distribution, metabolism, or excretion of drugs. * Illness within 30 days before screening. * History of hypersensitivity to calcium channel blockers. * Multiple drug allergies * Opioids (at doses exceeding the equivalent of 15 mg of oral morphine) or a high-dose capsaicin patch (Qutenza) \<=30 days before the screening visit. * Moderate or strong cytochrome P450 inducer within 30 days before the screening visit. * Digoxin or prohibited medications that cannot be discontinued before randomization. * Other exclusions apply.