Pharmacokinetic characterization of favipiravir in patients with COVID-19.

This prospective observational study describes the pharmacokinetic characteristics of favipiravir in adult patients hospitalized for mild to moderate COVID-19 with a positive RT-PCR test. Favipiravir was administered for 5 days, with a loading dose of 3200 mg and a maintenance dose of 1200 mg/day. Serial blood samples were collected on Day 2 and Day 4 of the therapy. Laboratory findings of the patients (n = 21) and in-hospital mortality were recorded. Favipiravir concentrations exhibited substantial variability and a significant decrease during the treatment of COVID-19. The median favipiravir trough concentration (C ) on Day 2 was 21.26 (interquartile range [IQR], 8.37-30.78) μg/mL, whereas it decreased significantly to 1.61 (IQR, 0.00-6.41) μg/mL on Day 4, the area under the concentration-time curve decreased by 68.5%. Day 2 C of female patients was higher than male patients. Our findings indicate that favipiravir concentrations show significant variability during the treatment of COVID-19 and therapeutic drug monitoring may be necessary to maintain targeted concentrations.