title: Lower clinical effectiveness of oseltamivir against influenza B contrasted with influenza A infection in children.
abstract: BACKGROUND
  Recently, many Japanese physicians have claimed that oseltamivir is less effective in children with influenza B virus infection. This study assesses the effectiveness of oseltamivir against influenza A (H3N2) and influenza B in children on the basis of the duration of febrile illness.
  
  
  METHODS
  We used oseltamivir to treat 127 children with influenza A (H3N2; mean age, 6.97 years [range, 1-15 years]) and 362 children with influenza B (mean age, 5.16 years [range, 1-15 years]) in outpatient clinics. The duration of fever after the start of oseltamivir therapy was compared in the influenza A group and the influenza B group.
  
  
  RESULTS
  The mean duration of fever after the start of oseltamivir therapy was significantly greater in the influenza B group than in the influenza A (H3N2) group (2.18 days vs. 1.31 days, respectively; P<.001). The difference was marked in young children (1-5 years old; 2.37 days for the influenza B group vs. 1.42 days for the influenza A group) but was not significant among older children (11-15 years old). The 50% inhibitory concentration of oseltamivir against influenza B virus was 75.4+/-41.7 nmol/L and was substantially higher than that for type A (H3N2) virus (0.3+/-0.1 nmol/L). Only 3 (1.6%) of 192 influenza B viruses were resistant to oseltamivir.
  
  
  CONCLUSIONS
  Oseltamivir is much less effective against influenza B virus infection in young children, probably because of the low sensitivity of influenza B viruses to oseltamivir. The effectiveness of oseltamivir against influenza B is influenced by age and host immunity. A few oseltamivir-resistant influenza B strains were isolated before the start of oseltamivir therapy.
authors.affiliation: Department of Pediatrics, Keiyu Hospital, Yokohama, Kanagawa, 220-0012, Japan. sugaya-n@za2.so-net.ne.jp
authors.forename: Norio
authors.initials: N
authors.lastname: Sugaya
authors.forename: Keiko
authors.initials: K
authors.lastname: Mitamura
authors.forename: Masahiko
authors.initials: M
authors.lastname: Yamazaki
authors.forename: Daisuke
authors.initials: D
authors.lastname: Tamura
authors.forename: Masataka
authors.initials: M
authors.lastname: Ichikawa
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Kimura
authors.forename: Chiharu
authors.initials: C
authors.lastname: Kawakami
authors.forename: Maki
authors.initials: M
authors.lastname: Kiso
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Ito
authors.forename: Shuji
authors.initials: S
authors.lastname: Hatakeyama
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kawaoka
mesh_terms: D000293:Adolescent; D000375:Aging; D000998:Antiviral Agents / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects*; D009981:Influenza B virus / Q000187:drug effects*; D007251:Influenza, Human / Q000188:drug therapy* / Q000821:virology*; D053139:Oseltamivir / Q000627:therapeutic use*
chemical_list: D000998:Antiviral Agents; D053139:Oseltamivir