Favipiravir

Favipiravir, sold under the brand name Avigan among others, is an antiviral medication used to treat influenza in Japan. It is also being studied to treat a number of other viral infections, including SARS-CoV-2. Like the experimental antiviral drugs T-1105 and T-1106, it is a pyrazinecarboxamide derivative.

It is being developed and manufactured by Toyama Chemical (a subsidiary of Fujifilm) and was approved for medical use in Japan in 2014. In 2016, Fujifilm licensed it to Zhejiang Hisun Pharmaceutical Co. It became a generic drug in 2019.

Medical use

Favipiravir has been approved to treat influenza in Japan. It is, however, only indicated for novel influenza (strains that cause more severe disease) rather than seasonal influenza. As of 2020, the probability of resistance developing appears low.

Side effects

There is evidence that use during pregnancy may result in harm to the baby. Teratogenic and embryotoxic effects were shown on four animal species. In one case report, a 6-month old infant developed benign bright blue discolouration of the cornea after treatment with favipiravir which resolved after treatment cessation.

Mechanism of action

The mechanism of its actions is thought to be related to the selective inhibition of viral RNA-dependent RNA polymerase. Favipiravir is a prodrug that is metabolized to its active form, favipiravir-ribofuranosyl-5'-triphosphate (favipiravir-RTP), available in both oral and intravenous formulations. In 2014, favipiravir was approved in Japan for stockpiling against influenza pandemics. However, favipiravir has not been shown to be effective in primary human airway cells, casting doubt on its efficacy in influenza treatment.