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Yukako KAGESHIMA, Eiichi INADA, Keisuke YAMAGUCHI, Masakazu HAYASHIDA120Objective: Herpes zoster (HZ) is a common disease, whose most common complication is postherpetic neuralgia (PHN). We conducted this study to compare effects of amenamevir (AMNV) and famciclovir (FCV) on intensities of acute HZ pain and the incidence of PHN, which have not been compared yet.Methods: After approval by the Ethics Committee, we retrospectively investigated adult patients with HZ treated with AMNV or FCV at Juntendo University Hospital between October, 2018 and February, 2020. We compared, between 143 AMNV-treated and 131 FCV-treated patients, pain scores of acute HZ pain evaluated on an 11-point numerical rating scale (NRS) and the incidence of PHN with the Mann-Whitney U test and Pearson’s chi-square test, respectively. The univariate logistic regression analysis was used to identify predictors of PHN.Results: Pain scores during the acute HZ period remained significantly lower in AMNV-treated patients than FCV-treated patients (p = 0.049, 0.011, and 0.016 for Day 3-4, Day 7, and Week 2-3, respectively), although the pain score at Day 0 before treatment didn’t differ between them (p > 0.05). The incidence of PHN didn’t differ between them (9.8 % vs. 11.5 %, p > 0.05). In the total cohort, the pain score at Week 2-3 was significantly associated with the development of PHN (r2 = 0.180, p < 0.00001).Conclusions: Compared with FCV, AMNV was more effective in reducing acute HZ pain, possibly reflecting its unique mechanism of action. However, AMNV didn’t reduce the incidence of PHN possibly due to the multifactorial etiology of PHN.Key words: amenamevir, famciclovir, herpes zoster, postherpetic neuralgia, zoster associated painJuntendo Medical Journal2022. 68(2), 120-130Original ArticlesA Comparison Between Effects of Amenamevir and Famciclovir on Intensities of Acute Pain and the Incidence of Postherpetic Neuralgia in Adult Patients with Herpes ZosterIntroductionTwenty-five percent of the whole population is affected by Herpes Zoster (HZ), of which the most common complication is postherpetic neuralgia (PHN)1). Famciclovir (FCV) is a guanine analog drug used as an antiherpetic agent, whose dose is not affected by renal function, unlike older drugs including valaciclovir (VACV)2-4). Reportedly, FCV prevents acute HZ pain more effectively than VACV5). Amenamevir (AMNV) is a newly-devel-oped helicase-primase inhibitor, which is capable of preventing formation of new skin lesions more effectively without producing worse side effects, Department of Anesthesiology and Pain Medicine, Juntendo University Graduate School of Medicine, Tokyo, JapanCorresponding author: Yukako KageshimaDepartment of Anesthesiology and Pain Medicine, Juntendo University Graduate School of Medicine2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, JapanTEL: +81-3-3813-3111　E-mail: y.kageshima1004@gmail.com, y-kageshima@juntendo.ac.jp〔Received　Nov. 2, 2021〕〔Accepted　Jan. 7, 2022〕J-STAGE Advance published date: Apr. 15, 2022Copyright © 2022 The Juntendo Medical Society. This is an open access article distributed under the terms of Creative Commons Attribution License (CC BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original source is properly credited. doi: 10.14789/jmj.JMJ21-0036-OAcompared with VACV6). To date, however, the effects of the newest antiherpetic agent AMNV and the second newest antiherpetic agent FCV on intensities of acute HZ pain and the incidence of PHN have not been compared. Therefore, we conducted the present study to compare the effects of AMNV and FCV on these two endpoints. Prior to this retrospective, observational study, the study protocol was reviewed and approved by the Ethics Committee of Juntendo University Hospital (approval number, 20-015) with a waiver of patients’ written informed consent.Methods