A review of the safety of favipiravir - a potential treatment in the COVID-19 pandemic?

ABSTRACT

BACKGROUND: Repurposing broad-spectrum antivirals is an immediate treatment opportunity for 2019 coronavirus disease (COVID-19). Favipiravir is an antiviral previously indicated for influenza and Ebola, which has shown some promise in early trials for treatment of COVID-19. We aim to review existing favipiravir safety evidence, which is vital to informing the potential future use of favipiravir in COVID-19. METHODS: A search was conducted across EMBASE and MEDLINE databases, supplemented by relevant grey-literature and ClinicalTrials.gov. All studies assessing the use of favipiravir in humans by 27 March 2020 were considered for inclusion. Further analysis of available safety data from phase 2 and 3 studies was undertaken. Data extracted were adverse events (AEs) grade 1-4, serious AEs and discontinuation for AEs. Specific AEs of interest highlighted in early-phase studies, including gastrointestinal AEs and hyperuricaemia, were also examined. RESULTS: Twenty-nine studies were identified as potential sources of evidence of the clinical safety of favipiravir. Six were phase 2 and 3 studies reporting relevant safety data for statistical comparison, representing a total of 4299 participants, an estimated 175 person-years-of-follow-up (PYFU). Comparator drugs were oseltamivir, umifenovir, lopinavir/ritonavir or placebo. Study follow-up was between 5 and 21 days. The proportions of grade 1-4 AEs on favipiravir was 28.2% vs 28.4% (P = n.s.) in the comparison arms. The proportion of discontinuations due to AEs on favipiravir was 1.1% vs 1.2% (P = n.s.) in the comparison arms. For serious AEs the proportion was 0.4% in both arms (P = n.s.). There were significantly fewer gastrointestinal AEs occurring on favipiravir vs comparators [8.7% vs 11.5%; P = 0.003]. Favipiravir showed significantly more uric acid elevations than comparators [5.8% vs 1.3%; P<0.0001]. CONCLUSIONS: Favipiravir demonstrates a favourable safety profile regarding total and serious AEs. However, safety concerns remain hyperuricaemia, teratogenicity and QTc prolongation have not yet been adequately studied. Favipiravir may be safe and tolerable in short-term use, but more evidence is needed to assess the longer-term effects of treatment. Given the limitations of the evidence and unresolved safety concerns, caution is warranted in the widespread use of favipiravir against pandemic COVID-19.