This study will compare Z160 and placebo in patients with Postherpetic Neuralgia for safety and efficacy for a period of 6 weeks.

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.