MDCK cells transfected with the human
beta-galactoside alpha-2,6-sialyltransferase 1 gene (AX-4 cells) were used to determine the
drug susceptibility and pharmacodynamically linked variable of
oseltamivir for influenza virus. For dose-ranging studies, five hollow-fiber units were charged with 10(2) A/Sydney/5/97 (H3N2) influenza virus-infected AX-4 cells and 10(8) uninfected AX-4 cells. Each unit was treated continuously with different
oseltamivir carboxylate concentrations in virus growth medium for 6 days. For dose fractionation studies, one hollow-fiber unit received no
drug, one unit received a 1x 50% effective concentration (EC(50)) exposure to
oseltamivir by continuous infusion, one unit received the same AUC(0-24) (area under the concentration-time curve from 0 to 24 h) by 1-h infusion every 24 h, one unit received the same total exposure in two equal fractions every 12 h, and one unit received the same total exposure in three equal fractions every 8 h. Each infusion dose was followed by a no-
drug washout, producing the appropriate half-life for this
drug. The effect of the
drug on virus replication was determined by sampling the units daily, measuring the amount of released virus by plaque assay, and performing a hemagglutination assay. The
drug concentration in the hollow-fiber
infection model systems was determined at various times by liquid chromatography-tandem mass spectrometry. The dose-ranging study showed that the EC(50)s for
oseltamivir carboxylate for the A/Sydney/5/97 strain of influenza virus was about 1.0 ng/ml. The dose fractionation study showed that all treatment arms suppressed virus replication to the same extent, indicating that the pharmacodynamically linked variable was the AUC(0-24)/EC(50) ratio. This implies that it may be possible to treat influenza virus
infection once daily with a dose of 150 mg/day.