An exploratory study of the efficacy and safety of amenamevir for the treatment of herpes zoster in patients receiving immunosuppressive drugs

Amenamevir is an oral once‐daily antiherpesvirus drug that can be administered without dose adjustment in patients with impaired renal function. There are currently no clinical data on immunocompromised patients with herpes zoster treated with amenamevir. Therefore, an exploratory study of the efficacy and safety of amenamevir against herpes zoster in patients with immunosuppression was conducted. Inclusion criteria included patients with acute herpes zoster receiving immunosuppressive drugs or those with malignant tumors or autoimmune diseases. Twenty‐four patients were included and received amenamevir (400 mg once daily after meals) for up to 14 days. The primary end point of overall improvement in skin symptoms 7 days after treatment initiation (day 7) was 58.3% for “markedly improved” and 20.8% for “improved.” The combined improvement rate was 79.2% (95% confidence interval, 57.8–92.9), and 20.8% of patients experienced “worsened” symptoms. The secondary end points of overall improvement in skin symptoms on day 14 and day 28 were 95.7% and 100%, respectively. The skin symptoms progressed during treatment, peaking on day 7, and then began to heal. By Kaplan–Meier estimation, the median periods to complete crusting and healing were both day 14. There were five adverse events with a possible causal relationship to amenamevir (bacterial skin infection, anemia, hyponatremia, headache, and abnormal liver function) in one of the 24 patients. Although the bacterial skin infection was severe, all events in this patient were reported to be either recovered or recovering. These findings indicate that amenamevir can be effective and safe in immunocompromised patients with herpes zoster. However, as worsening can happen around day 7, it is necessary to carefully monitor such patients and switch to other therapies such as intravenous acyclovir if necessary. Clinical trial identifier: Japan Registry of Clinical Trials jRCTs031190208.