[Efficacy and safety of the selective oral neuraminidase inhibitor oseltamivir for prophylaxis against influenza--placebo-controlled double-blind multicenter phase III trial].

: We have investigated the long-term prophylactic efficacy and safety of oseltamivir phosphate (Ro64-0796), an orally bioavailable prodrug of novel, potent and selective type A and type B influenzavirus neuraminidase inhibitor, when Ro64-0796 was administered orally to the healthy volunteers. Participants older than 16 year-old were randomly assigned to either Ro64-0796 75 mg once daily group or matching placebo group for six weeks. A total of 308 participants (Placebo group; 153 and Ro64-0796 group; 155) were enrolled in this trial. The primary variable of efficacy, incidence of laboratory-confirmed influenzavirus infected subjects accompanied by both fever of 37.5 degrees C or higher and at least two influenza symptoms (group 1) were 1.3% in Ro64-0796 group in contrast with 8.5% in placebo group, inducing 85% inhibition of infection (p = 0.00323, Fisher's exact test). As secondary variable, incidence of laboratory-confirmed influenzavirus infected subjects who lack either fever (37.5 degrees C or higher) or at least two influenza symptoms (group 2) and incidence of asymptomatic infected subjects (group 3) were tend to decrease in Ro64-0796 group, and finally cumulative inhibition rate was 76% in group 1 + 2 combined (p = 0.000891. Fisher's exact test), and 63% in group 1 + 2 + 3 combined (p = 0.002150, Fisher's exact test). As for the safety evaluations, Ro64-0796 was well tolerated but was associated with gastrointestinal disorders such as nausea and vomiting which were mild and allowable for the clinical use. There was no abnormal change attributable to Ro64-0796 application in the clinical laboratory tests as well as the physiological tests. Our results demonstrate that oseltamivir is safe and effective for the prevention of influenza.