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Prospective Study of Treatment with Ensitrelvir for COVID-19 in Patients Undergoing Hemodialysis (PROTECT-HD)

Mineaki Kitamura¹, Takahiro Takazono², Naoki Hosogaya^3,4

¹Department of Nephrology, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.

Infectious Diseases and Therapy

|April 1, 2026

Insights

Ensitrelvir is safe and effective for mild COVID-19 patients on hemodialysis (HD). No dose adjustment is needed, showing stable plasma concentrations and favorable clinical outcomes without adverse events.

Area of Science:

Pharmacology
Virology
Nephrology

Background:

Patients on hemodialysis (HD) face increased COVID-19 vulnerability and trial exclusion.
Ensitrelvir, an oral SARS-CoV-2 protease inhibitor, lacked evaluation in HD patients.
This study addresses the need for COVID-19 treatment options in this population.

Purpose of the Study:

To assess ensitrelvir pharmacokinetics in mild COVID-19 patients undergoing HD.
To evaluate the antiviral activity, safety, and clinical effectiveness of ensitrelvir.
To determine if HD affects ensitrelvir plasma concentrations and if dose adjustment is necessary.

Main Methods:

Prospective, single-arm, open-label study (December 2024-April 2025).
Participants received ensitrelvir (375 mg Day 1, then 125 mg daily Days 2-5).
Plasma concentrations measured pre- and post-dialysis; clinical outcomes, viral load monitored.

Main Results:

Eight participants (mean age 68.1 years) completed the study.
Stable plasma ensitrelvir concentrations observed before (18.0 µg/mL) and after dialysis (16.4 µg/mL).
Clinical effectiveness noted by Day 8; viral load declined; no serious adverse events occurred.

Conclusions:

Ensitrelvir demonstrated stable pharmacokinetics in HD patients, similar to healthy individuals.
Favorable antiviral and clinical responses support ensitrelvir's use without dose adjustment in this population.
Ensitrelvir is a safe and effective option for mild COVID-19 patients on hemodialysis.

Read full analysis

Abstract

Introduction:

Patients on hemodialysis (HD) are vulnerable to COVID-19 and often excluded from pivotal antiviral trials. Ensitrelvir, an oral SARS-CoV-2 3C-like protease inhibitor approved in Japan, remains unevaluated in patients undergoing HD. This study assesses the pharmacokinetics, antiviral activity, safety, and clinical effectiveness of ensitrelvir in participants with mild COVID-19 undergoing HD.

Methods:

In this prospective, single-arm, open-label study (December 2024-April 2025), participants with mild COVID-19 undergoing HD received ensitrelvir 375 mg on Day 1, followed by 125 mg once daily on Days 2-5. On Visit 2 (Day 3), plasma ensitrelvir concentrations were measured at three time points prior to ensitrelvir administration-before, during, and after dialysis. On Visit 3 (Day 5), blood samples were collected after dialysis and prior to ensitrelvir administration. Clinical outcomes, body temperature, SARS-CoV-2 viral load, and viral titers were monitored through Day 8. The primary endpoint was plasma concentration of ensitrelvir relative to dialysis; secondary endpoints included clinical outcomes, body temperature, and changes in viral load.

Results:

Eight participants were evaluated: mean age, 68.1 years; mean body weight, 58.0 kg; and mean body mass index, 24.1 kg/m². Plasma ensitrelvir concentrations (geometric mean) remained stable, with similar levels before (18.0 µg/mL) and after dialysis (16.4 µg/mL). All participants were judged clinically effective by the investigator by Day 8. Body temperature normalized within 16.6-48.0 h in four participants, and in one participant after 59.2 h. SARS-CoV-2 viral load (mean ± standard deviation) declined by 2.85 ± 1.52 log₁₀ copies/mL from baseline to Day 8. No treatment-emergent adverse events, hospitalizations, or severe COVID-19-related complications occurred.

Conclusion:

No dose adjustment was required regardless of HD. In participants with mild COVID-19 undergoing HD, plasma ensitrelvir concentrations were similar to those previously reported in healthy individuals. Ensitrelvir showed favorable antiviral and clinical responses, supporting its safe use without dose adjustments.

Trial Registration:

Japan Registry of Clinical Trials ID: jRCTs071240069.

Keywords:

Antiviral therapy COVID-19 Ensitrelvir Hemodialysis Japan Pharmacokinetics Renal impairment SARS-CoV-2

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