Evaluation of Analgesic Effect of Lidocaine Patch 5% in Post-herpetic Neuralgia: An Interventional Study

Abstract

Introduction: Herpes Zoster (HZ) is a very painful and debilitating condition caused by the reactivation of the Varicella Zoster Virus (VZV). HZ is characterised by a maculopapular or vesicular rash, usually accompanied by pain that is unilateral and restricted to dermatomes. Post-herpatic Neuralgia (PHN) is defined as pain that persists for more than 90 days after the onset of the HZ rash. Aim: To evaluate the analgesic efficacy of a lidocaine patch in PHN. Materials and Methods: This prospective interventional study conducted at the Department of Anaesthesiology and Critical Care, Pt. BD Sharma, PGIMS, Rohtak, Haryana, India, from February 2020 to March 2021. The study included a total of 24 patients (single group), with a male-to-female ratio of 11:13, aged between 18 and 75 years, all with a Visual Analogue Scale (VAS) score greater than 4. An evaluation of patient pain scores using the VAS and the total number of lidocaine patches used per week for four weeks or until the VAS declined to four was conducted. After obtaining informed and written consent, a medicated 5% lidocaine patch was applied to cover the appropriate area for a minimum period of 12 hours, followed by removal for the next 12 hours. This application continued until the VAS declined to four or up to a maximum of four weeks. The level of significance was set at p≤0.05. Results: In the present study, a total of 24 patients were included. The mean age was 59.5±12.85 years, with 54.2% being female and 45.8% male. The VAS scores at baseline were 8.71±0.999, which reduced to 7.08±1.349 at the end of one week, 5.67±0.007 at the end of two weeks, 4.25±0.442 at the end of three weeks and 3.58±0.830 at the end of four weeks. The VAS scores were significantly lower in all patients over the four weeks (p=0.001). The total number of patches used was 1.88±0.338 at one week, 1.46±0.509 at two weeks, 1.04±0.204 at three weeks and 1.00 at four weeks. The total amount of patches used was significantly reduced over the four weeks (p=0.001). No side-effects related to the lidocaine patch were noted. Conclusion: The 5% lidocaine patch demonstrated good tolerability with a minimal risk of systemic adverse drug reactions and is an effective modality for relieving moderate to severe pain. It is concluded that the 5% lidocaine patch is very effective in the treatment of PHN.