Antiviral Effect of Favipiravir (T-705) against Measles and Subacute Sclerosing Panencephalitis Viruses.

Subacute sclerosing panencephalitis (SSPE) is a late-onset, intractable, and fatal viral disease caused by persistent infection of the central nervous system with a measles virus mutant (SSPE virus). In Japan, interferon-α and ribavirin are administered intracerebroventricularly to patients with SSPE. However, as the therapeutic effect is insufficient, more effective drugs are needed. Favipiravir, which is clinically used as an anti-influenza drug, demonstrates anti-viral effects against RNA viruses. In this study, the antiviral effect of favipiravir against measles virus (Edmonston strain) and SSPE virus (Yamagata-1 strain) was examined in vitro. The 50% effective concentration (EC50) of favipiravir (inhibiting viral plaque formation by 50%) against Edmonston and Yamagata-1 strains were 108.7 ± 2.0 μM (17.1 ± 0.3 μg/mL) and 38.6 ± 6.0 μM (6.1 ± 0.9 μg/mL), respectively, which were similar to those of ribavirin. The antiviral activity of favipiravir against the SSPE virus was demonstrated for the first time in this study.