Favipiravir for the treatment of COVID-19 pneumonia: Can we predict the response to treatment?

Introduction: Early experience with favipiravir in the treatment of COVID-19 is promising, but no clinical data have been published in medical journals. This study aimed to review the experience with favipiravir treatment for COVID-19 pneumonia and to examine whether there are any predictors of treatment response.

Methodology: Fifty-six patients with severe or progressive pneumonia associated with COVID-19 who were treated with favipiravir monotherapy for at least five days were included in this retrospective study. Treatment response was defined as clinical recovery without any need for admission into the intensive care unit and/or anti-cytokine therapy. The demographic, clinical, laboratory and radiographic features of the patients were compared between favipiravir-responders and non-responders.

Results: Of the 56 patients, 34 patients (60.7%) responded to treatment and recovered. There was no difference in the demographic, clinical, and radiographic findings between the responders and non-responders. The inflammatory biomarkers were also similar except for the CRP levels on the day favipiravir was started [74 (36-111) vs. 118.5 (46.5-203) mg/L, respectively, p = 0.043]. There was also a significant difference in the median time to defervescence [1 (1-2) vs. 3.5 (1.75-9.25) days, respectively]. Of clinical interest, 27 (79.4%) and 31 (91.2%) of the responders became afebrile within two and four days, respectively. The response rate was lower in patients who presented severe pneumonia associated with respiratory failure.

Conclusions: Patients with non-severe pneumonia at admission and whose fever resolved within two days of treatment are more likely to improve with favipiravir.