TABLE 1.

Inhibition of the enzyme activity of the reference viruses in the NAI assay with NA-Star substrate

Virus strainVirus NA type/subtypeNA mutationMean IC50 ± SD (nM) (fold increase)c
OseltamivirZanamivir
B/Memphis/20/96B2.01 ± 0.694.10 ± 1.79
    Zanamivir-selected mutantaBR152K77.24 ± 23.94 (38)40.99 ± 27.88 (10)
B/Rochester/2/2001B3.82 ± 1.964.39 ± 1.82
    Oseltamivir-selected mutantaBD198N28.92 ± 9.37 (8)42.08 ± 22.14 (10)
A/Texas/36/91 (H1N1)A/N11.06 ± 0.361.55 ± 0.22
    Oseltamivir-selected mutantA/N1H274Y260.25 ± 55.82 (246)2.41 ± 0.81 (2)
A/turkey/Minnesota/833/80 (H4N2)A/N20.82 ± 0.344.26 ± 2.17
    Zanamivir-selected mutantA/N2R292K795.50 ± 196.24 (970)6.36 ± 1.37 (1.5)
    Zanamivir-selected mutantA/N2E119G0.93 ± 0.71 (1)33.48 ± 6.41 (8)
    Zanamivir-selected mutantA/N2E119A1.44 ± 1.04 (2)17.82 ± 4.87 (4)
    Zanamivir-selected mutantA/N2E119D1.21 ± 0.72 (1)71.52 ± 16.79 (17)
A/Bethesda/956/2006 (H3N2) oseltamivir-selected mutanta,bA/N2R292K480.64 ± 217.2995.24 ± 2.31
  • a Viruses were recovered from an immunocompromised patient.

  • b A matching drug-sensitive virus was unavailable.

  • c Boldface indicates IC50s that are above the cutoff values (mean + 3 standard deviations [SD]) determined for the seasonal influenza A and B viruses in the present study. Mean ± SD were calculated from data collected from at least three independent experiments.