A Study With Lido-Patch and Placebo Plaster in Patients Suffering From Postherpetic Neuralgia (PHN)

Inclusion Criteria for the Run-in Phase: * Adult participants, male and female, with a minimum age of 50 years at screening. * Participants who had postherpetic neuralgia (PHN) for at least 3 months after healing of a herpes zoster skin rash. * Pain score of at least 4, based on an 11-point numerical rating scale (NRS) (scale of 0-10), at the screening and enrolment visit. The pain assessment is the participant's recall of the pain intensity since the previous week. * Written informed consent given. Randomization Criteria: * Participants must be regularly (minimum every second day) using the Lido-Patch for control of pain in the last 4 weeks of the run-in phase. The participant must wait for pain to increase before applying a new patch. * The participants' average daily pain intensity (with patch on) must be 7 or less on an 11-point NRS (scale of 0-10), and must increase during the phases when a patch is not worn, during Week 8 of the Run-in Phase. * Before randomization, the participant must have an average relief with Lido-Patch of "moderate" or better, on a 6-item scale (worse, no pain relief, slight, moderate, a lot, complete) during Week 8 of the Run-in Phase. Exclusion Criteria: * Participation in another study of investigational drugs or devices parallel to, or less than 30 days before screening, or previous participation in this study. * Known to or suspected of not being able to comply with the study protocol. * Any clinically significant condition that would, in the investigator's opinion, preclude study participation for instance alcohol, medication or drug dependency, neurotic personality, psychiatric illness, epilepsy or suicide risk. * Pregnancy or nursing mother. * Woman in childbearing age without satisfactory contraception. * Hypersensitivity to lidocaine or amide-type local anesthetic drugs. * Active herpes zoster lesion or dermatitis of any origin at the affected site with PHN. * Evidence of another cause for pain in the area affected by herpes zoster in addition to PHN, such as lumbar radiculopathy, surgery or trauma, if this could confound assessment or self-evaluation of the pain due to post herpetic neuralgia. * Participants who had neurological ablation by block or neurosurgical intervention for control of pain in PHN. * Participants using topically applied analgesic compounds on the PHN affected area. * Presence of other severe pain that could confound assessment or self-evaluation of the pain due to PHN. * Participants with severe hepatic disorder and/or alanine or aspartate aminotransferase equal to or above 3-fold the upper limit of normal (ULN). * Participants with severe renal disorder and/or increased serum creatinine equal to or above 1.5-fold the upper limit of normal (ULN). * Participants who are undergoing active treatment for cancer, are known to be infected with the human immunodeficiency virus (HIV), or being acutely and intensively immunosuppressed following transplantation.