Favipiravir, also known as T-705, is an antiviral drug that has been approved in 
2014 in Japan to treat pandemic influenza virus infections. The drug is 
converted intracellularly into its active, phosphoribosylated form, which is 
recognized as a substrate by the viral RNA-dependent RNA polymerase. 
Interestingly, besides its anti-influenza virus activity, this molecule is also 
able to inhibit the replication of flavi-, alpha-, filo-, bunya-, arena-, noro-, 
and of other RNA viruses, which include neglected and (re)emerging viruses for 
which no antiviral therapy is currently available. We will discuss the potential 
of favipiravir as a broad-spectrum countermeasure against infections caused by 
such neglected RNA viruses. Favipiravir has already been used off-label to treat 
patients infected with the Ebola virus and the Lassa virus. Because of the 
particular set-up of the clinical trials during these outbreaks, clear 
conclusions on the efficacy of favipiravir could not be made. For several 
viruses, it was demonstrated that the barrier of resistance development against 
favipiravir is high. Favipiravir has been shown to be well tolerated in healthy 
volunteers and in influenza virus-infected patients; however, caution is needed 
because of the teratogenic risks of this molecule. Because of its antiviral 
activity against different RNA viruses and its high barrier for resistance, the 
potential of favipiravir as a broad-spectrum antiviral seems promising, but 
safety and potency issues should be overcome before this drug or similar 
molecules could be used to treat large patient groups.