The relationship between plasma favipiravir concentrations and clinical outcomes in COVID-19
File(s)
Published version
Author(s)
Type
Journal Article
Abstract
Background
Favipiravir has shown efficacy against SARS-CoV-2 in patients <60 years old, but data linking plasma concentrations to clinical outcomes are limited. This study investigated whether favipiravir plasma concentrations influence clinical efficacy and outcomes in patients hospitalised with COVID-19. The main research question was, How can antiviral dosing strategies be optimised to improve pandemic preparedness and treatment efficacy?
Methods
Adult participants were drawn from the PIONEER trial, in which patients received oral favipiravir (1800 mg twice daily for 1 day, then 800 mg twice daily for 9 days) plus standard care. This analysis included patients with confirmed COVID-19 and ≥75% study adherence. Samples were collected between days 5 and 10 post-treatment initiation. The primary outcome was time to clinical improvement. Secondary outcomes included achievement of clinical improvement and mortality risk.
Results
Out of 140 patients (50% male; mean±sd age 59.5±14.8 years), target plasma concentrations were reached in 29 (21%). Mean time to improvement was 7.7±5.9 days in target achievers versus 9.1±7.2 days in non-achievers (p=0.26). The target was more often achieved in female (34%) than male (7%) participants (p=0.0002). Plasma concentration inversely correlated with body mass index (r= –0.4, p<0.0001), and with lower body mass index in achievers (26.0±5.1 kg·m−2 versus 30.5±6.9 kg·m−2, p=0.003). Alkaline phosphatase and alanine aminotransferase levels were also lower in achievers (p=0.004 and p=0.02, respectively).
Conclusion
Most patients did not reach target favipiravir levels. Concentrations were influenced by sex, body mass index and liver function, confirming the need for pharmacokinetically guided dosing and therapeutic monitoring to optimise antiviral efficacy in future pandemic responses.
Favipiravir has shown efficacy against SARS-CoV-2 in patients <60 years old, but data linking plasma concentrations to clinical outcomes are limited. This study investigated whether favipiravir plasma concentrations influence clinical efficacy and outcomes in patients hospitalised with COVID-19. The main research question was, How can antiviral dosing strategies be optimised to improve pandemic preparedness and treatment efficacy?
Methods
Adult participants were drawn from the PIONEER trial, in which patients received oral favipiravir (1800 mg twice daily for 1 day, then 800 mg twice daily for 9 days) plus standard care. This analysis included patients with confirmed COVID-19 and ≥75% study adherence. Samples were collected between days 5 and 10 post-treatment initiation. The primary outcome was time to clinical improvement. Secondary outcomes included achievement of clinical improvement and mortality risk.
Results
Out of 140 patients (50% male; mean±sd age 59.5±14.8 years), target plasma concentrations were reached in 29 (21%). Mean time to improvement was 7.7±5.9 days in target achievers versus 9.1±7.2 days in non-achievers (p=0.26). The target was more often achieved in female (34%) than male (7%) participants (p=0.0002). Plasma concentration inversely correlated with body mass index (r= –0.4, p<0.0001), and with lower body mass index in achievers (26.0±5.1 kg·m−2 versus 30.5±6.9 kg·m−2, p=0.003). Alkaline phosphatase and alanine aminotransferase levels were also lower in achievers (p=0.004 and p=0.02, respectively).
Conclusion
Most patients did not reach target favipiravir levels. Concentrations were influenced by sex, body mass index and liver function, confirming the need for pharmacokinetically guided dosing and therapeutic monitoring to optimise antiviral efficacy in future pandemic responses.
Date Issued
2026-07-01
Date Acceptance
2026-01-26
Citation
ERJ Open Research, 2026, 12 (4)
ISSN
2312-0541
Publisher
European Respiratory Society
Journal / Book Title
ERJ Open Research
Volume
12
Issue
4
Copyright Statement
©The authors 2026. This version is distributed under the terms of the Creative Commons Attribution Licence 4.0.
License URL
Identifier
10.1183/23120541.01560-2025
Publication Status
Published
Article Number
01560-2025
Date Publish Online
2026-03-26