Characterization of susceptibility variants of influenza virus grown in the presence of T-705

T-705 (favipiravir) is a potent inhibitor of rna polymerases of influenza viruses. susceptibility variants were isolated during passages in the presence of t-705. nine variants with 0.4 to 2.1 times the 50% inhibitory concentration for plaque formation of the parent a/pr/8/34 (h1n1) strain had amino acid variations in the pb1,pb2,and pa genes of the rna polymerase complex. however,the variation patterns in the rna polymerase complex indicated that t-705 does not work as a mutagen,and resistant mutants were not isolated,possibly because a mutation leading to resistance would be lethal to the rna polymerase function. © the japanese pharmacological society.