We estimated the efficacy of the current single administration of
peramivir on the basis of
peramivir pharmacokinetics in the upper respiratory tract (URT) and determined the predictive
peramivir concentration-time curve to assess its efficacy against viruses with decreased susceptibility to
neuraminidase inhibitors. Serum, nasal swab, or aspiration samples were collected from 28 patients treated with 10 mg/kg
body weight peramivir. The sequential
influenza viral RNA load and susceptibility after
peramivir administration were measured using a quantitative real-time reverse transcription-PCR and
neuraminidase inhibition assay. The
peramivir concentrations in the serum and URT after a single administration
at 10 mg/kg were measured, and the predictive blood and URT
peramivir concentration-time curves were determined to assess various administration regimens against resistant variants. The
peramivir concentration decreased to <0.1% of the maximum concentration of
drug in serum (Cmax) at 24 h after administration. Rapid elimination of
peramivir from the URT by 48 h after administration may contribute to an increase in the
influenza A viral load after day 3 but not to a decrease in the
influenza B viral load, despite the absence of a decrease in the susceptibility to
peramivir. A longer maintenance of a high level of
peramivir in the URT is expected by divided administration rather than once-daily administration. When no clinical improvement is observed in patients with normal susceptibility
influenza A and B,
peramivir readministration should be considered. In severe cases caused by resistant variants, better inhibitory effectiveness and less frequent adverse events are expected by divided administration rather than once-daily administration with an increased dosage.