Zanamivir animal studies, conducted primarily in rabbits, showed a trend towards increased post-implantation loss, decreased fetal body weight, and increased minor fetal skeletal changes, although these effects were not statistically significant. Given the frequency, pattern and distribution of these effects, it was concluded that they were not related to zanamivir treatment. The summary of product characteristics for zanamivir states that it should not be used during pregnancy unless the potential benefit to the mother justifies the risk to the fetus.